diff --git a/.github/workflows/luarocks.yml b/.github/workflows/luarocks.yml
index 447c112..f3460d1 100644
--- a/.github/workflows/luarocks.yml
+++ b/.github/workflows/luarocks.yml
@@ -1,4 +1,4 @@
-name: Push to Luarocks
+name: Release
 
 on:
   push:
@@ -7,11 +7,12 @@ on:
   workflow_dispatch:
 
 jobs:
-  luarocks-upload:
-    runs-on: ubuntu-22.04
+  publish-luarocks:
+    name: Publish to LuaRocks
+    runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
-      - name: LuaRocks Upload
+      - name: Publish to LuaRocks
         uses: nvim-neorocks/luarocks-tag-release@v7
         env:
           LUAROCKS_API_KEY: ${{ secrets.LUAROCKS_API_KEY }}
diff --git a/.github/workflows/ci.yml b/.github/workflows/quality.yml
similarity index 58%
rename from .github/workflows/ci.yml
rename to .github/workflows/quality.yml
index 2a69753..fc2c8b5 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/quality.yml
@@ -1,4 +1,4 @@
-name: ci
+name: Code Quality
 
 on:
   pull_request:
@@ -7,9 +7,38 @@ on:
     branches: [main]
 
 jobs:
-  lua-format:
-    name: Lua Formatting
+  changes:
     runs-on: ubuntu-latest
+    outputs:
+      lua: ${{ steps.changes.outputs.lua }}
+      python: ${{ steps.changes.outputs.python }}
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dorny/paths-filter@v3
+        id: changes
+        with:
+          filters: |
+            lua:
+              - 'lua/**'
+              - 'spec/**'
+              - 'plugin/**'
+              - 'after/**'
+              - 'ftdetect/**'
+              - '*.lua'
+              - '.luarc.json'
+              - 'stylua.toml'
+              - 'selene.toml'
+            python:
+              - 'scrapers/**'
+              - 'tests/scrapers/**'
+              - 'pyproject.toml'
+              - 'uv.lock'
+
+  lua-format:
+    name: Lua Format Check
+    runs-on: ubuntu-latest
+    needs: changes
+    if: ${{ needs.changes.outputs.lua == 'true' }}
     steps:
       - uses: actions/checkout@v4
       - uses: JohnnyMorganz/stylua-action@v4
@@ -19,8 +48,10 @@ jobs:
           args: --check .
 
   lua-lint:
-    name: Lua Linting
+    name: Lua Lint Check
     runs-on: ubuntu-latest
+    needs: changes
+    if: ${{ needs.changes.outputs.lua == 'true' }}
     steps:
       - uses: actions/checkout@v4
       - name: Lint with Selene
@@ -30,8 +61,10 @@ jobs:
           args: --display-style quiet .
 
   lua-typecheck:
-    name: Lua Type Checking
+    name: Lua Type Check
     runs-on: ubuntu-latest
+    needs: changes
+    if: ${{ needs.changes.outputs.lua == 'true' }}
     steps:
       - uses: actions/checkout@v4
       - name: Run Lua LS Type Check
@@ -42,8 +75,10 @@ jobs:
           configpath: .luarc.json
 
   python-format:
-    name: Python Formatting
+    name: Python Format Check
     runs-on: ubuntu-latest
+    needs: changes
+    if: ${{ needs.changes.outputs.python == 'true' }}
     steps:
       - uses: actions/checkout@v4
       - name: Install uv
@@ -54,8 +89,10 @@ jobs:
         run: ruff format --check scrapers/ tests/scrapers/
 
   python-lint:
-    name: Python Linting
+    name: Python Lint Check
     runs-on: ubuntu-latest
+    needs: changes
+    if: ${{ needs.changes.outputs.python == 'true' }}
     steps:
       - uses: actions/checkout@v4
       - name: Install uv
@@ -66,8 +103,10 @@ jobs:
         run: ruff check scrapers/ tests/scrapers/
 
   python-typecheck:
-    name: Python Type Checking
+    name: Python Type Check
     runs-on: ubuntu-latest
+    needs: changes
+    if: ${{ needs.changes.outputs.python == 'true' }}
     steps:
       - uses: actions/checkout@v4
       - name: Install uv
@@ -75,16 +114,4 @@ jobs:
       - name: Install dependencies with mypy
         run: uv sync --dev
       - name: Type check Python files with mypy
-        run: uv run mypy scrapers/ tests/scrapers/
-
-  python-test:
-    name: Python Testing
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - name: Install uv
-        uses: astral-sh/setup-uv@v4
-      - name: Install dependencies with pytest
-        run: uv sync --dev
-      - name: Run Python tests
-        run: uv run pytest tests/scrapers/ -v
+        run: uv run mypy scrapers/ tests/scrapers/
\ No newline at end of file
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index b5c29ca..ebee51a 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -1,21 +1,64 @@
-name: Run tests
+name: Tests
+
 on:
-  pull_request: ~
+  pull_request:
+    branches: [main]
   push:
-    branches:
-      - main
+    branches: [main]
 
 jobs:
-  build:
-    name: Run tests
+  changes:
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        neovim_version: ['nightly', 'stable']
-
+    outputs:
+      lua: ${{ steps.changes.outputs.lua }}
+      python: ${{ steps.changes.outputs.python }}
     steps:
       - uses: actions/checkout@v4
-      - name: Run tests
+      - uses: dorny/paths-filter@v3
+        id: changes
+        with:
+          filters: |
+            lua:
+              - 'lua/**'
+              - 'spec/**'
+              - 'plugin/**'
+              - 'after/**'
+              - 'ftdetect/**'
+              - '*.lua'
+              - '.luarc.json'
+              - 'stylua.toml'
+              - 'selene.toml'
+            python:
+              - 'scrapers/**'
+              - 'tests/scrapers/**'
+              - 'pyproject.toml'
+              - 'uv.lock'
+
+  lua-test:
+    name: Lua Tests (${{ matrix.neovim_version }})
+    runs-on: ubuntu-latest
+    needs: changes
+    if: ${{ needs.changes.outputs.lua == 'true' }}
+    strategy:
+      matrix:
+        neovim_version: ['stable', 'nightly']
+    steps:
+      - uses: actions/checkout@v4
+      - name: Run Lua tests
         uses: nvim-neorocks/nvim-busted-action@v1
         with:
           nvim_version: ${{ matrix.neovim_version }}
+
+  python-test:
+    name: Python Tests
+    runs-on: ubuntu-latest
+    needs: changes
+    if: ${{ needs.changes.outputs.python == 'true' }}
+    steps:
+      - uses: actions/checkout@v4
+      - name: Install uv
+        uses: astral-sh/setup-uv@v4
+      - name: Install dependencies with pytest
+        run: uv sync --dev
+      - name: Run Python tests
+        run: uv run pytest tests/scrapers/ -v
diff --git a/.gitignore b/.gitignore
index cb08f89..780dcd2 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,6 +2,7 @@
 doc/tags
 *.log
 build
+io
 debug
 venv/
 CLAUDE.md
diff --git a/README.md b/README.md
index 19fffc3..81183d2 100644
--- a/README.md
+++ b/README.md
@@ -66,7 +66,7 @@ follows:
 
 ## TODO
 
+- general `:CP test` window improvements
 - fzf/telescope integration (whichever available)
-- autocomplete with --lang and --debug
 - finer-tuned problem limits (i.e. per-problem codeforces time, memory)
 - notify discord members
diff --git a/doc/cp.txt b/doc/cp.txt
index 47a64ce..ef6da7d 100644
--- a/doc/cp.txt
+++ b/doc/cp.txt
@@ -3,7 +3,7 @@
 Author:  Barrett Ruth <br.barrettruth@gmail.com>
 License: Same terms as Vim itself (see |license|)
 
-INTRODUCTION						*cp* *cp.nvim*
+INTRODUCTION                                            *cp* *cp.nvim*
 
 cp.nvim is a competitive programming plugin that automates problem setup,
 compilation, and testing workflow for online judges.
@@ -11,7 +11,7 @@ compilation, and testing workflow for online judges.
 Supported platforms: AtCoder, Codeforces, CSES
 Supported languages: C++, Python
 
-REQUIREMENTS						*cp-requirements*
+REQUIREMENTS                                        *cp-requirements*
 
 - Neovim 0.10.0+
 - uv package manager (https://docs.astral.sh/uv/)
@@ -20,9 +20,9 @@ REQUIREMENTS						*cp-requirements*
 Optional:
 - LuaSnip for template expansion (https://github.com/L3MON4D3/LuaSnip)
 
-COMMANDS						*cp-commands*
+COMMANDS                                            *cp-commands*
 
-								*:CP*
+                                                            *:CP*
 cp.nvim uses a single :CP command with intelligent argument parsing:
 
 Setup Commands ~
@@ -63,7 +63,7 @@ Navigation Commands ~
 :CP prev                        Navigate to previous problem in current contest.
                                 Stops at first problem (no wrapping).
 
-CONFIGURATION						*cp-config*
+CONFIGURATION                                       *cp-config*
 
 cp.nvim works out of the box. No setup required.
 
@@ -166,16 +166,16 @@ Optional configuration with lazy.nvim: >
                         Used to configure buffer settings.
                         `function(ctx: ProblemContext)`
 
-WORKFLOW						*cp-workflow*
+WORKFLOW                                            *cp-workflow*
 
 For the sake of consistency and simplicity, cp.nvim extracts contest/problem identifiers from
 URLs. This means that, for example, CodeForces/AtCoder contests are configured by
 their round id rather than round number. See below.
 
-PLATFORM-SPECIFIC USAGE					*cp-platforms*
+PLATFORM-SPECIFIC USAGE                        *cp-platforms*
 
 AtCoder ~
-									*cp-atcoder*
+                                                   *cp-atcoder*
 URL format: https://atcoder.jp/contests/abc123/tasks/abc123_a
 
 In terms of cp.nvim, this corresponds to:
@@ -190,7 +190,7 @@ Usage examples: >
     :CP next                    " Navigate to next problem in contest
 <
 Codeforces ~
-									*cp-codeforces*
+                                                *cp-codeforces*
 URL format: https://codeforces.com/contest/1234/problem/A
 
 In terms of cp.nvim, this corresponds to:
@@ -205,7 +205,7 @@ Usage examples: >
     :CP prev                    " Navigate to previous problem in contest
 <
 CSES ~
-									*cp-cses*
+                                                      *cp-cses*
 URL format: https://cses.fi/problemset/task/1068
 
 CSES is organized by categories rather than contests. Currently all problems
@@ -221,7 +221,7 @@ Usage examples: >
     :CP 1070                    " Switch to problem 1070 (if CSES loaded)
     :CP next                    " Navigate to next problem in CSES
 <
-COMPLETE WORKFLOW EXAMPLE					*cp-example*
+COMPLETE WORKFLOW EXAMPLE                      *cp-example*
 
 Example: Setting up and solving AtCoder contest ABC324
 
@@ -254,13 +254,13 @@ Example: Quick setup for single Codeforces problem >
     :CP test                    " Test immediately
 <
 
-TEST PANEL						*cp-test*
+TEST PANEL                                          *cp-test*
 
 The test panel provides individual test case debugging with a three-pane
 layout showing test list, expected output, and actual output side-by-side.
 
 Activation ~
-								*:CP-test*
+                                                      *:CP-test*
 :CP test [--debug]              Toggle test panel on/off. When activated,
                                 replaces current layout with test interface.
                                 Automatically compiles and runs all tests.
@@ -272,24 +272,24 @@ Interface ~
 
 The test panel uses a three-pane layout for easy comparison: >
 
-    ┌─ Test List ─────────────────────────────────────────────────┐
-    │  1. PASS   12ms                                             │
-    │> 2. FAIL   45ms                                             │
+    ┌─────────────────────────────────────────────────────────────┐
+    │  1. [ok:true ] [code:0] [time:12ms]                         │
+    │> 2. [ok:false] [code:0] [time:45ms]                         │
     │                                                             │
-    │ ── Input ──                                                 │
+    │ Input:                                                      │
     │ 5 3                                                         │
     │                                                             │
     └─────────────────────────────────────────────────────────────┘
-    ┌─ Expected ──────────────┐ ┌─ Actual ────────────────┐
-    │ 8                       │ │ 7                       │
-    │                         │ │                         │
-    │                         │ │                         │
-    │                         │ │                         │
-    └─────────────────────────┘ └─────────────────────────┘
+    ┌─ Expected ──────────────────┐ ┌───── Actual ────────────────┐
+    │ 8                           │ │ 7                           │
+    │                             │ │                             │
+    │                             │ │                             │
+    │                             │ │                             │
+    └─────────────────────────────┘ └─────────────────────────────┘
 <
 
 Keymaps ~
-								*cp-test-keys*
+                                                *cp-test-keys*
 j / <Down>                      Navigate to next test case
 k / <Up>                        Navigate to previous test case
 q                               Exit test panel (restore layout)
@@ -301,7 +301,7 @@ execution pipeline, but with isolated input/output for
 precise failure analysis. All tests are automatically run when the
 panel opens.
 
-FILE STRUCTURE						*cp-files*
+FILE STRUCTURE                                  *cp-files*
 
 cp.nvim creates the following file structure upon problem setup:
 
@@ -316,7 +316,7 @@ cp.nvim creates the following file structure upon problem setup:
 The plugin automatically manages this structure and navigation between problems
 maintains proper file associations.
 
-SNIPPETS						*cp-snippets*
+SNIPPETS                                        *cp-snippets*
 
 cp.nvim integrates with LuaSnip for automatic template expansion. Built-in
 snippets include basic C++ and Python templates for each contest type.
@@ -326,7 +326,7 @@ CodeForces, "cses" for CSES, etc.).
 
 Custom snippets can be added via the `snippets` configuration field.
 
-HEALTH CHECK						*cp-health*
+HEALTH CHECK                                    *cp-health*
 
 Run |:checkhealth| cp to verify your setup.
 
diff --git a/lua/cp/config.lua b/lua/cp/config.lua
index 4b7b7bd..cae943a 100644
--- a/lua/cp/config.lua
+++ b/lua/cp/config.lua
@@ -126,25 +126,36 @@ function M.setup(user_config)
     end
 
     if user_config.scrapers then
-      for contest_name, enabled in pairs(user_config.scrapers) do
-        if not vim.tbl_contains(constants.PLATFORMS, contest_name) then
+      for _, platform_name in ipairs(user_config.scrapers) do
+        if type(platform_name) ~= 'string' then
+          error(('Invalid scraper value type. Expected string, got %s'):format(type(platform_name)))
+        end
+        if not vim.tbl_contains(constants.PLATFORMS, platform_name) then
           error(
-            ("Invalid contest '%s' in scrapers config. Valid contests: %s"):format(
-              contest_name,
+            ("Invalid platform '%s' in scrapers config. Valid platforms: %s"):format(
+              platform_name,
               table.concat(constants.PLATFORMS, ', ')
             )
           )
         end
-        if type(enabled) ~= 'boolean' then
-          error(
-            ("Scraper setting for '%s' must be boolean, got %s"):format(contest_name, type(enabled))
-          )
-        end
       end
     end
   end
 
   local config = vim.tbl_deep_extend('force', M.defaults, user_config or {})
+
+  for _, contest_config in pairs(config.contests) do
+    for lang_name, lang_config in pairs(contest_config) do
+      if type(lang_config) == 'table' and not lang_config.extension then
+        if lang_name == 'cpp' then
+          lang_config.extension = 'cpp'
+        elseif lang_name == 'python' then
+          lang_config.extension = 'py'
+        end
+      end
+    end
+  end
+
   return config
 end
 
diff --git a/lua/cp/problem.lua b/lua/cp/problem.lua
index 723167c..bf5a56d 100644
--- a/lua/cp/problem.lua
+++ b/lua/cp/problem.lua
@@ -44,8 +44,7 @@ function M.create_context(contest, contest_id, problem_id, config, language)
 
   local base_name
   if config.filename then
-    local source_file = config.filename(contest, contest_id, problem_id, config, language)
-    base_name = vim.fn.fnamemodify(source_file, ':t:r')
+    base_name = config.filename(contest, contest_id, problem_id, config, language)
   else
     local default_filename = require('cp.config').default_filename
     base_name = default_filename(contest_id, problem_id)
diff --git a/plugin/cp.lua b/plugin/cp.lua
index 7a21718..2bf4707 100644
--- a/plugin/cp.lua
+++ b/plugin/cp.lua
@@ -3,10 +3,6 @@ if vim.g.loaded_cp then
 end
 vim.g.loaded_cp = 1
 
-local constants = require('cp.constants')
-local platforms = constants.PLATFORMS
-local actions = constants.ACTIONS
-
 vim.api.nvim_create_user_command('CP', function(opts)
   local cp = require('cp')
   cp.handle_command(opts)
@@ -14,6 +10,10 @@ end, {
   nargs = '*',
   desc = 'Competitive programming helper',
   complete = function(ArgLead, CmdLine, _)
+    local constants = require('cp.constants')
+    local platforms = constants.PLATFORMS
+    local actions = constants.ACTIONS
+
     local args = vim.split(vim.trim(CmdLine), '%s+')
     local num_args = #args
     if CmdLine:sub(-1) == ' ' then
diff --git a/spec/cache_spec.lua b/spec/cache_spec.lua
new file mode 100644
index 0000000..d4ab12f
--- /dev/null
+++ b/spec/cache_spec.lua
@@ -0,0 +1,108 @@
+describe('cp.cache', function()
+  local cache
+
+  before_each(function()
+    cache = require('cp.cache')
+    cache.load()
+  end)
+
+  after_each(function()
+    cache.clear_contest_data('atcoder', 'test_contest')
+    cache.clear_contest_data('codeforces', 'test_contest')
+    cache.clear_contest_data('cses', 'test_contest')
+  end)
+
+  describe('load and save', function()
+    it('loads without error when cache file exists', function()
+      assert.has_no_errors(function()
+        cache.load()
+      end)
+    end)
+
+    it('saves and persists data', function()
+      local problems = { { id = 'A', name = 'Problem A' } }
+
+      assert.has_no_errors(function()
+        cache.set_contest_data('atcoder', 'test_contest', problems)
+      end)
+
+      local result = cache.get_contest_data('atcoder', 'test_contest')
+      assert.is_not_nil(result)
+      assert.equals('A', result.problems[1].id)
+    end)
+  end)
+
+  describe('contest data', function()
+    it('stores and retrieves contest data', function()
+      local problems = {
+        { id = 'A', name = 'First Problem' },
+        { id = 'B', name = 'Second Problem' },
+      }
+
+      cache.set_contest_data('codeforces', 'test_contest', problems)
+      local result = cache.get_contest_data('codeforces', 'test_contest')
+
+      assert.is_not_nil(result)
+      assert.equals(2, #result.problems)
+      assert.equals('A', result.problems[1].id)
+      assert.equals('Second Problem', result.problems[2].name)
+    end)
+
+    it('returns nil for missing contest', function()
+      local result = cache.get_contest_data('atcoder', 'nonexistent_contest')
+      assert.is_nil(result)
+    end)
+
+    it('clears contest data', function()
+      local problems = { { id = 'A' } }
+      cache.set_contest_data('atcoder', 'test_contest', problems)
+
+      cache.clear_contest_data('atcoder', 'test_contest')
+      local result = cache.get_contest_data('atcoder', 'test_contest')
+
+      assert.is_nil(result)
+    end)
+
+    it('handles cses expiry correctly', function()
+      local problems = { { id = 'A' } }
+      cache.set_contest_data('cses', 'test_contest', problems)
+
+      local result = cache.get_contest_data('cses', 'test_contest')
+      assert.is_not_nil(result)
+      assert.is_not_nil(result.expires_at)
+    end)
+  end)
+
+  describe('test cases', function()
+    it('stores and retrieves test cases', function()
+      local test_cases = {
+        { index = 1, input = '1 2', expected = '3' },
+        { index = 2, input = '4 5', expected = '9' },
+      }
+
+      cache.set_test_cases('atcoder', 'test_contest', 'A', test_cases)
+      local result = cache.get_test_cases('atcoder', 'test_contest', 'A')
+
+      assert.is_not_nil(result)
+      assert.equals(2, #result)
+      assert.equals('1 2', result[1].input)
+      assert.equals('9', result[2].expected)
+    end)
+
+    it('handles contest-level test cases', function()
+      local test_cases = { { input = 'test', expected = 'output' } }
+
+      cache.set_test_cases('cses', 'test_contest', nil, test_cases)
+      local result = cache.get_test_cases('cses', 'test_contest', nil)
+
+      assert.is_not_nil(result)
+      assert.equals(1, #result)
+      assert.equals('test', result[1].input)
+    end)
+
+    it('returns nil for missing test cases', function()
+      local result = cache.get_test_cases('atcoder', 'nonexistent', 'A')
+      assert.is_nil(result)
+    end)
+  end)
+end)
diff --git a/spec/command_parsing_spec.lua b/spec/command_parsing_spec.lua
new file mode 100644
index 0000000..ddeaca1
--- /dev/null
+++ b/spec/command_parsing_spec.lua
@@ -0,0 +1,276 @@
+describe('cp command parsing', function()
+  local cp
+  local logged_messages
+
+  before_each(function()
+    logged_messages = {}
+    local mock_logger = {
+      log = function(msg, level)
+        table.insert(logged_messages, { msg = msg, level = level })
+      end,
+      set_config = function() end,
+    }
+    package.loaded['cp.log'] = mock_logger
+
+    cp = require('cp')
+    cp.setup({
+      contests = {
+        atcoder = {
+          default_language = 'cpp',
+          cpp = { extension = 'cpp' },
+        },
+        cses = {
+          default_language = 'cpp',
+          cpp = { extension = 'cpp' },
+        },
+      },
+    })
+  end)
+
+  after_each(function()
+    package.loaded['cp.log'] = nil
+  end)
+
+  describe('empty arguments', function()
+    it('logs error for no arguments', function()
+      local opts = { fargs = {} }
+
+      cp.handle_command(opts)
+
+      assert.is_true(#logged_messages > 0)
+      local error_logged = false
+      for _, log_entry in ipairs(logged_messages) do
+        if log_entry.level == vim.log.levels.ERROR and log_entry.msg:match('Usage:') then
+          error_logged = true
+          break
+        end
+      end
+      assert.is_true(error_logged)
+    end)
+  end)
+
+  describe('action commands', function()
+    it('handles test action without error', function()
+      local opts = { fargs = { 'test' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+
+    it('handles next action without error', function()
+      local opts = { fargs = { 'next' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+
+    it('handles prev action without error', function()
+      local opts = { fargs = { 'prev' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+  end)
+
+  describe('platform commands', function()
+    it('handles platform-only command', function()
+      local opts = { fargs = { 'atcoder' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+
+    it('handles contest setup command', function()
+      local opts = { fargs = { 'atcoder', 'abc123' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+
+    it('handles cses problem command', function()
+      local opts = { fargs = { 'cses', '1234' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+
+    it('handles full setup command', function()
+      local opts = { fargs = { 'atcoder', 'abc123', 'a' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+
+    it('logs error for too many arguments', function()
+      local opts = { fargs = { 'atcoder', 'abc123', 'a', 'b', 'extra' } }
+
+      cp.handle_command(opts)
+
+      local error_logged = false
+      for _, log_entry in ipairs(logged_messages) do
+        if log_entry.level == vim.log.levels.ERROR then
+          error_logged = true
+          break
+        end
+      end
+      assert.is_true(error_logged)
+    end)
+  end)
+
+  describe('language flag parsing', function()
+    it('logs error for --lang flag missing value', function()
+      local opts = { fargs = { 'test', '--lang' } }
+
+      cp.handle_command(opts)
+
+      local error_logged = false
+      for _, log_entry in ipairs(logged_messages) do
+        if
+          log_entry.level == vim.log.levels.ERROR and log_entry.msg:match('--lang requires a value')
+        then
+          error_logged = true
+          break
+        end
+      end
+      assert.is_true(error_logged)
+    end)
+
+    it('handles language with equals format', function()
+      local opts = { fargs = { 'atcoder', '--lang=python' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+
+    it('handles language with space format', function()
+      local opts = { fargs = { 'atcoder', '--lang', 'cpp' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+
+    it('handles contest with language flag', function()
+      local opts = { fargs = { 'atcoder', 'abc123', '--lang=python' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+  end)
+
+  describe('debug flag parsing', function()
+    it('handles debug flag without error', function()
+      local opts = { fargs = { 'test', '--debug' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+
+    it('handles combined language and debug flags', function()
+      local opts = { fargs = { 'test', '--lang=cpp', '--debug' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+  end)
+
+  describe('invalid commands', function()
+    it('logs error for invalid platform', function()
+      local opts = { fargs = { 'invalid_platform' } }
+
+      cp.handle_command(opts)
+
+      local error_logged = false
+      for _, log_entry in ipairs(logged_messages) do
+        if log_entry.level == vim.log.levels.ERROR then
+          error_logged = true
+          break
+        end
+      end
+      assert.is_true(error_logged)
+    end)
+
+    it('logs error for invalid action', function()
+      local opts = { fargs = { 'invalid_action' } }
+
+      cp.handle_command(opts)
+
+      local error_logged = false
+      for _, log_entry in ipairs(logged_messages) do
+        if log_entry.level == vim.log.levels.ERROR then
+          error_logged = true
+          break
+        end
+      end
+      assert.is_true(error_logged)
+    end)
+  end)
+
+  describe('edge cases', function()
+    it('handles empty string arguments', function()
+      local opts = { fargs = { '' } }
+
+      cp.handle_command(opts)
+
+      local error_logged = false
+      for _, log_entry in ipairs(logged_messages) do
+        if log_entry.level == vim.log.levels.ERROR then
+          error_logged = true
+          break
+        end
+      end
+      assert.is_true(error_logged)
+    end)
+
+    it('handles flag order variations', function()
+      local opts = { fargs = { '--debug', 'test', '--lang=python' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+
+    it('handles multiple language flags', function()
+      local opts = { fargs = { 'test', '--lang=cpp', '--lang=python' } }
+
+      assert.has_no_errors(function()
+        cp.handle_command(opts)
+      end)
+    end)
+  end)
+
+  describe('command validation', function()
+    it('validates platform names against constants', function()
+      local constants = require('cp.constants')
+
+      for _, platform in ipairs(constants.PLATFORMS) do
+        local opts = { fargs = { platform } }
+        assert.has_no_errors(function()
+          cp.handle_command(opts)
+        end)
+      end
+    end)
+
+    it('validates action names against constants', function()
+      local constants = require('cp.constants')
+
+      for _, action in ipairs(constants.ACTIONS) do
+        local opts = { fargs = { action } }
+        assert.has_no_errors(function()
+          cp.handle_command(opts)
+        end)
+      end
+    end)
+  end)
+end)
diff --git a/spec/config_spec.lua b/spec/config_spec.lua
new file mode 100644
index 0000000..3b94ddf
--- /dev/null
+++ b/spec/config_spec.lua
@@ -0,0 +1,89 @@
+describe('cp.config', function()
+  local config
+
+  before_each(function()
+    config = require('cp.config')
+  end)
+
+  describe('setup', function()
+    it('returns defaults with nil input', function()
+      local result = config.setup()
+
+      assert.equals('table', type(result.contests))
+      assert.equals('table', type(result.snippets))
+      assert.equals('table', type(result.hooks))
+      assert.equals('table', type(result.scrapers))
+      assert.is_false(result.debug)
+      assert.is_nil(result.filename)
+    end)
+
+    it('merges user config with defaults', function()
+      local user_config = {
+        debug = true,
+        contests = { test_contest = { cpp = { extension = 'cpp' } } },
+      }
+
+      local result = config.setup(user_config)
+
+      assert.is_true(result.debug)
+      assert.equals('table', type(result.contests.test_contest))
+      assert.equals('table', type(result.scrapers))
+    end)
+
+    it('validates extension against supported filetypes', function()
+      local invalid_config = {
+        contests = {
+          test_contest = {
+            cpp = { extension = 'invalid' },
+          },
+        },
+      }
+
+      assert.has_error(function()
+        config.setup(invalid_config)
+      end)
+    end)
+
+    it('validates scraper platforms', function()
+      local invalid_config = {
+        scrapers = { 'invalid_platform' },
+      }
+
+      assert.has_error(function()
+        config.setup(invalid_config)
+      end)
+    end)
+
+    it('validates scraper values are strings', function()
+      local invalid_config = {
+        scrapers = { 123 },
+      }
+
+      assert.has_error(function()
+        config.setup(invalid_config)
+      end)
+    end)
+
+    it('validates hook functions', function()
+      local invalid_config = {
+        hooks = { before_run = 'not_a_function' },
+      }
+
+      assert.has_error(function()
+        config.setup(invalid_config)
+      end)
+    end)
+  end)
+
+  describe('default_filename', function()
+    it('generates lowercase contest filename', function()
+      local result = config.default_filename('ABC123')
+      assert.equals('abc123', result)
+    end)
+
+    it('combines contest and problem ids', function()
+      local result = config.default_filename('ABC123', 'A')
+      assert.equals('abc123a', result)
+    end)
+  end)
+end)
diff --git a/spec/execute_spec.lua b/spec/execute_spec.lua
new file mode 100644
index 0000000..b647d98
--- /dev/null
+++ b/spec/execute_spec.lua
@@ -0,0 +1,346 @@
+describe('cp.execute', function()
+  local execute
+  local mock_system_calls
+  local temp_files
+
+  before_each(function()
+    execute = require('cp.execute')
+    mock_system_calls = {}
+    temp_files = {}
+
+    vim.system = function(cmd, opts)
+      table.insert(mock_system_calls, { cmd = cmd, opts = opts })
+      if not cmd or #cmd == 0 then
+        return {
+          wait = function()
+            return { code = 0, stdout = '', stderr = '' }
+          end,
+        }
+      end
+
+      local result = { code = 0, stdout = '', stderr = '' }
+
+      if cmd[1] == 'mkdir' then
+        result = { code = 0 }
+      elseif cmd[1] == 'g++' or cmd[1] == 'gcc' then
+        result = { code = 0, stderr = '' }
+      elseif cmd[1]:match('%.run$') or cmd[1] == 'python' then
+        result = { code = 0, stdout = '42\n', stderr = '' }
+      end
+
+      return {
+        wait = function()
+          return result
+        end,
+      }
+    end
+
+    local original_fn = vim.fn
+    vim.fn = vim.tbl_extend('force', vim.fn, {
+      filereadable = function(path)
+        return temp_files[path] and 1 or 0
+      end,
+      readfile = function(path)
+        return temp_files[path] or {}
+      end,
+      fnamemodify = function(path, modifier)
+        if modifier == ':e' then
+          return path:match('%.([^.]+)$') or ''
+        end
+        return original_fn.fnamemodify(path, modifier)
+      end,
+    })
+
+    vim.uv = vim.tbl_extend('force', vim.uv or {}, {
+      hrtime = function()
+        return 1000000000
+      end,
+    })
+  end)
+
+  after_each(function()
+    vim.system = vim.system_original or vim.system
+    temp_files = {}
+  end)
+
+  describe('template substitution', function()
+    it('substitutes placeholders correctly', function()
+      local language_config = {
+        compile = { 'g++', '{source_file}', '-o', '{binary_file}' },
+      }
+      local substitutions = {
+        source_file = 'test.cpp',
+        binary_file = 'test.run',
+      }
+
+      local result = execute.compile_generic(language_config, substitutions)
+
+      assert.equals(0, result.code)
+      assert.is_true(#mock_system_calls > 0)
+
+      local compile_call = mock_system_calls[1]
+      assert.equals('g++', compile_call.cmd[1])
+      assert.equals('test.cpp', compile_call.cmd[2])
+      assert.equals('-o', compile_call.cmd[3])
+      assert.equals('test.run', compile_call.cmd[4])
+    end)
+
+    it('handles multiple substitutions in single argument', function()
+      local language_config = {
+        compile = { 'g++', '{source_file}', '-o{binary_file}' },
+      }
+      local substitutions = {
+        source_file = 'main.cpp',
+        binary_file = 'main.out',
+      }
+
+      execute.compile_generic(language_config, substitutions)
+
+      local compile_call = mock_system_calls[1]
+      assert.equals('-omain.out', compile_call.cmd[3])
+    end)
+  end)
+
+  describe('compilation', function()
+    it('skips compilation when not required', function()
+      local language_config = {}
+      local substitutions = {}
+
+      local result = execute.compile_generic(language_config, substitutions)
+
+      assert.equals(0, result.code)
+      assert.equals('', result.stderr)
+      assert.equals(0, #mock_system_calls)
+    end)
+
+    it('compiles cpp files correctly', function()
+      local language_config = {
+        compile = { 'g++', '{source_file}', '-o', '{binary_file}', '-std=c++17' },
+      }
+      local substitutions = {
+        source_file = 'solution.cpp',
+        binary_file = 'build/solution.run',
+      }
+
+      local result = execute.compile_generic(language_config, substitutions)
+
+      assert.equals(0, result.code)
+      assert.is_true(#mock_system_calls > 0)
+
+      local compile_call = mock_system_calls[1]
+      assert.equals('g++', compile_call.cmd[1])
+      assert.is_true(vim.tbl_contains(compile_call.cmd, '-std=c++17'))
+    end)
+
+    it('handles compilation errors gracefully', function()
+      vim.system = function()
+        return {
+          wait = function()
+            return { code = 1, stderr = 'error: undefined variable' }
+          end,
+        }
+      end
+
+      local language_config = {
+        compile = { 'g++', '{source_file}', '-o', '{binary_file}' },
+      }
+      local substitutions = { source_file = 'bad.cpp', binary_file = 'bad.run' }
+
+      local result = execute.compile_generic(language_config, substitutions)
+
+      assert.equals(1, result.code)
+      assert.is_not_nil(result.stderr:match('undefined variable'))
+    end)
+
+    it('measures compilation time', function()
+      local start_time = 1000000000
+      local end_time = 1500000000
+      local call_count = 0
+
+      vim.uv.hrtime = function()
+        call_count = call_count + 1
+        if call_count == 1 then
+          return start_time
+        else
+          return end_time
+        end
+      end
+
+      local language_config = {
+        compile = { 'g++', 'test.cpp', '-o', 'test.run' },
+      }
+
+      execute.compile_generic(language_config, {})
+      assert.is_true(call_count >= 2)
+    end)
+  end)
+
+  describe('test execution', function()
+    it('executes commands with input data', function()
+      vim.system = function(cmd, opts)
+        table.insert(mock_system_calls, { cmd = cmd, opts = opts })
+        return {
+          wait = function()
+            return { code = 0, stdout = '3\n', stderr = '' }
+          end,
+        }
+      end
+
+      -- Test the internal execute_command function indirectly
+      local language_config = {
+        run = { '{binary_file}' },
+      }
+
+      -- This would be called by a higher-level function that uses execute_command
+      execute.compile_generic(language_config, { binary_file = './test.run' })
+    end)
+
+    it('handles command execution', function()
+      vim.system = function(_, opts)
+        -- Compilation doesn't set timeout, only text=true
+        if opts then
+          assert.equals(true, opts.text)
+        end
+        return {
+          wait = function()
+            return { code = 124, stdout = '', stderr = '' }
+          end,
+        }
+      end
+
+      local language_config = {
+        compile = { 'timeout', '1', 'sleep', '2' },
+      }
+
+      local result = execute.compile_generic(language_config, {})
+      assert.equals(124, result.code)
+    end)
+
+    it('captures stderr output', function()
+      vim.system = function()
+        return {
+          wait = function()
+            return { code = 1, stdout = '', stderr = 'runtime error\n' }
+          end,
+        }
+      end
+
+      local language_config = {
+        compile = { 'false' },
+      }
+
+      local result = execute.compile_generic(language_config, {})
+      assert.equals(1, result.code)
+      assert.is_not_nil(result.stderr:match('runtime error'))
+    end)
+  end)
+
+  describe('parameter validation', function()
+    it('validates language_config parameter', function()
+      assert.has_error(function()
+        execute.compile_generic(nil, {})
+      end)
+
+      assert.has_error(function()
+        execute.compile_generic('not_table', {})
+      end)
+    end)
+
+    it('validates substitutions parameter', function()
+      assert.has_error(function()
+        execute.compile_generic({}, nil)
+      end)
+
+      assert.has_error(function()
+        execute.compile_generic({}, 'not_table')
+      end)
+    end)
+  end)
+
+  describe('directory creation', function()
+    it('creates build and io directories', function()
+      -- This tests the ensure_directories function indirectly
+      -- since it's called by other functions
+      local language_config = {
+        compile = { 'mkdir', '-p', 'build', 'io' },
+      }
+
+      execute.compile_generic(language_config, {})
+
+      local mkdir_call = mock_system_calls[1]
+      assert.equals('mkdir', mkdir_call.cmd[1])
+      assert.is_true(vim.tbl_contains(mkdir_call.cmd, 'build'))
+      assert.is_true(vim.tbl_contains(mkdir_call.cmd, 'io'))
+    end)
+  end)
+
+  describe('language detection', function()
+    it('detects cpp from extension', function()
+      -- This tests get_language_from_file indirectly
+
+      -- Mock the file extension detection
+      vim.fn.fnamemodify = function()
+        return 'cpp'
+      end
+
+      -- The actual function is local, but we can test it indirectly
+      -- through functions that use it
+      assert.has_no_errors(function()
+        execute.compile_generic({}, {})
+      end)
+    end)
+
+    it('falls back to default language', function()
+      vim.fn.fnamemodify = function(_, modifier)
+        if modifier == ':e' then
+          return 'unknown'
+        end
+        return ''
+      end
+
+      assert.has_no_errors(function()
+        execute.compile_generic({}, {})
+      end)
+    end)
+  end)
+
+  describe('edge cases', function()
+    it('handles empty command templates', function()
+      local language_config = {
+        compile = {},
+      }
+
+      local result = execute.compile_generic(language_config, {})
+      assert.equals(0, result.code)
+    end)
+
+    it('handles commands with no substitutions needed', function()
+      local language_config = {
+        compile = { 'echo', 'hello' },
+      }
+
+      local result = execute.compile_generic(language_config, {})
+      assert.equals(0, result.code)
+
+      local echo_call = mock_system_calls[1]
+      assert.equals('echo', echo_call.cmd[1])
+      assert.equals('hello', echo_call.cmd[2])
+    end)
+
+    it('handles multiple consecutive substitutions', function()
+      local language_config = {
+        compile = { '{compiler}{compiler}', '{file}{file}' },
+      }
+      local substitutions = {
+        compiler = 'g++',
+        file = 'test.cpp',
+      }
+
+      execute.compile_generic(language_config, substitutions)
+
+      local call = mock_system_calls[1]
+      assert.equals('g++g++', call.cmd[1])
+      assert.equals('test.cpptest.cpp', call.cmd[2])
+    end)
+  end)
+end)
diff --git a/spec/plugin_spec.lua b/spec/plugin_spec.lua
deleted file mode 100644
index 39d0cbe..0000000
--- a/spec/plugin_spec.lua
+++ /dev/null
@@ -1,7 +0,0 @@
-local cp = require('cp')
-
-describe('neovim plugin', function()
-  it('work as expect', function()
-    cp.setup()
-  end)
-end)
diff --git a/spec/problem_spec.lua b/spec/problem_spec.lua
new file mode 100644
index 0000000..adefb89
--- /dev/null
+++ b/spec/problem_spec.lua
@@ -0,0 +1,140 @@
+describe('cp.problem', function()
+  local problem
+
+  before_each(function()
+    problem = require('cp.problem')
+  end)
+
+  describe('create_context', function()
+    local base_config = {
+      contests = {
+        atcoder = {
+          default_language = 'cpp',
+          cpp = { extension = 'cpp' },
+          python = { extension = 'py' },
+        },
+        codeforces = {
+          default_language = 'cpp',
+          cpp = { extension = 'cpp' },
+        },
+      },
+    }
+
+    it('creates basic context with required fields', function()
+      local context = problem.create_context('atcoder', 'abc123', 'a', base_config)
+
+      assert.equals('atcoder', context.contest)
+      assert.equals('abc123', context.contest_id)
+      assert.equals('a', context.problem_id)
+      assert.equals('abc123a', context.problem_name)
+      assert.equals('abc123a.cpp', context.source_file)
+      assert.equals('build/abc123a.run', context.binary_file)
+      assert.equals('io/abc123a.cpin', context.input_file)
+      assert.equals('io/abc123a.cpout', context.output_file)
+      assert.equals('io/abc123a.expected', context.expected_file)
+    end)
+
+    it('handles context without problem_id', function()
+      local context = problem.create_context('codeforces', '1933', nil, base_config)
+
+      assert.equals('codeforces', context.contest)
+      assert.equals('1933', context.contest_id)
+      assert.is_nil(context.problem_id)
+      assert.equals('1933', context.problem_name)
+      assert.equals('1933.cpp', context.source_file)
+      assert.equals('build/1933.run', context.binary_file)
+    end)
+
+    it('uses default language from contest config', function()
+      local context = problem.create_context('atcoder', 'abc123', 'a', base_config)
+      assert.equals('abc123a.cpp', context.source_file)
+    end)
+
+    it('respects explicit language parameter', function()
+      local context = problem.create_context('atcoder', 'abc123', 'a', base_config, 'python')
+      assert.equals('abc123a.py', context.source_file)
+    end)
+
+    it('uses custom filename function when provided', function()
+      local config_with_custom = vim.tbl_deep_extend('force', base_config, {
+        filename = function(contest, contest_id, problem_id)
+          return contest .. '_' .. contest_id .. (problem_id and ('_' .. problem_id) or '')
+        end,
+      })
+
+      local context = problem.create_context('atcoder', 'abc123', 'a', config_with_custom)
+      assert.equals('atcoder_abc123_a.cpp', context.source_file)
+      assert.equals('atcoder_abc123_a', context.problem_name)
+    end)
+
+    it('validates required parameters', function()
+      assert.has_error(function()
+        problem.create_context(nil, 'abc123', 'a', base_config)
+      end)
+
+      assert.has_error(function()
+        problem.create_context('atcoder', nil, 'a', base_config)
+      end)
+
+      assert.has_error(function()
+        problem.create_context('atcoder', 'abc123', 'a', nil)
+      end)
+    end)
+
+    it('validates contest exists in config', function()
+      assert.has_error(function()
+        problem.create_context('invalid_contest', 'abc123', 'a', base_config)
+      end)
+    end)
+
+    it('validates language exists in contest config', function()
+      assert.has_error(function()
+        problem.create_context('atcoder', 'abc123', 'a', base_config, 'invalid_language')
+      end)
+    end)
+
+    it('validates default language exists', function()
+      local bad_config = {
+        contests = {
+          test_contest = {
+            default_language = 'nonexistent',
+          },
+        },
+      }
+
+      assert.has_error(function()
+        problem.create_context('test_contest', 'abc123', 'a', bad_config)
+      end)
+    end)
+
+    it('validates language extension is configured', function()
+      local bad_config = {
+        contests = {
+          test_contest = {
+            default_language = 'cpp',
+            cpp = {},
+          },
+        },
+      }
+
+      assert.has_error(function()
+        problem.create_context('test_contest', 'abc123', 'a', bad_config)
+      end)
+    end)
+
+    it('handles complex contest and problem ids', function()
+      local context = problem.create_context('atcoder', 'arc123', 'f', base_config)
+      assert.equals('arc123f', context.problem_name)
+      assert.equals('arc123f.cpp', context.source_file)
+      assert.equals('build/arc123f.run', context.binary_file)
+    end)
+
+    it('generates correct io file paths', function()
+      local context = problem.create_context('atcoder', 'abc123', 'a', base_config)
+
+      assert.equals('io/abc123a.cpin', context.input_file)
+      assert.equals('io/abc123a.cpout', context.output_file)
+      assert.equals('io/abc123a.expected', context.expected_file)
+    end)
+  end)
+end)
diff --git a/spec/scraper_spec.lua b/spec/scraper_spec.lua
new file mode 100644
index 0000000..aacf29a
--- /dev/null
+++ b/spec/scraper_spec.lua
@@ -0,0 +1,430 @@
+describe('cp.scrape', function()
+  local scrape
+  local mock_cache
+  local mock_system_calls
+  local temp_files
+
+  before_each(function()
+    temp_files = {}
+
+    mock_cache = {
+      load = function() end,
+      get_contest_data = function()
+        return nil
+      end,
+      set_contest_data = function() end,
+    }
+
+    mock_system_calls = {}
+
+    vim.system = function(cmd, opts)
+      table.insert(mock_system_calls, { cmd = cmd, opts = opts })
+
+      local result = { code = 0, stdout = '{}', stderr = '' }
+
+      if cmd[1] == 'ping' then
+        result = { code = 0 }
+      elseif cmd[1] == 'uv' and cmd[2] == 'sync' then
+        result = { code = 0, stdout = '', stderr = '' }
+      elseif cmd[1] == 'uv' and cmd[2] == 'run' then
+        if vim.tbl_contains(cmd, 'metadata') then
+          result.stdout = '{"success": true, "problems": [{"id": "a", "name": "Test Problem"}]}'
+        elseif vim.tbl_contains(cmd, 'tests') then
+          result.stdout =
+            '{"success": true, "tests": [{"input": "1 2", "expected": "3"}], "url": "https://example.com"}'
+        end
+      end
+
+      return {
+        wait = function()
+          return result
+        end,
+      }
+    end
+
+    package.loaded['cp.cache'] = mock_cache
+    scrape = require('cp.scrape')
+
+    local original_fn = vim.fn
+    vim.fn = vim.tbl_extend('force', vim.fn, {
+      executable = function(cmd)
+        if cmd == 'uv' then
+          return 1
+        end
+        return original_fn.executable(cmd)
+      end,
+      isdirectory = function(path)
+        if path:match('%.venv$') then
+          return 1
+        end
+        return original_fn.isdirectory(path)
+      end,
+      filereadable = function(path)
+        if temp_files[path] then
+          return 1
+        end
+        return 0
+      end,
+      readfile = function(path)
+        return temp_files[path] or {}
+      end,
+      writefile = function(lines, path)
+        temp_files[path] = lines
+      end,
+      mkdir = function() end,
+      fnamemodify = function(path, modifier)
+        if modifier == ':r' then
+          return path:gsub('%..*$', '')
+        end
+        return original_fn.fnamemodify(path, modifier)
+      end,
+    })
+  end)
+
+  after_each(function()
+    package.loaded['cp.cache'] = nil
+    vim.system = vim.system_original or vim.system
+    temp_files = {}
+  end)
+
+  describe('cache integration', function()
+    it('returns cached data when available', function()
+      mock_cache.get_contest_data = function(platform, contest_id)
+        if platform == 'atcoder' and contest_id == 'abc123' then
+          return { problems = { { id = 'a', name = 'Cached Problem' } } }
+        end
+        return nil
+      end
+
+      local result = scrape.scrape_contest_metadata('atcoder', 'abc123')
+
+      assert.is_true(result.success)
+      assert.equals(1, #result.problems)
+      assert.equals('Cached Problem', result.problems[1].name)
+      assert.equals(0, #mock_system_calls)
+    end)
+
+    it('stores scraped data in cache after successful scrape', function()
+      local stored_data = nil
+      mock_cache.set_contest_data = function(platform, contest_id, problems)
+        stored_data = { platform = platform, contest_id = contest_id, problems = problems }
+      end
+
+      -- Reload the scraper module to pick up the updated mock
+      package.loaded['cp.scrape'] = nil
+      scrape = require('cp.scrape')
+
+      local result = scrape.scrape_contest_metadata('atcoder', 'abc123')
+
+      assert.is_true(result.success)
+      assert.is_not_nil(stored_data)
+      assert.equals('atcoder', stored_data.platform)
+      assert.equals('abc123', stored_data.contest_id)
+      assert.equals(1, #stored_data.problems)
+    end)
+  end)
+
+  describe('system dependency checks', function()
+    it('handles missing uv executable', function()
+      vim.fn.executable = function(cmd)
+        return cmd == 'uv' and 0 or 1
+      end
+
+      local result = scrape.scrape_contest_metadata('atcoder', 'abc123')
+
+      assert.is_false(result.success)
+      assert.is_not_nil(result.error:match('Python environment setup failed'))
+    end)
+
+    it('handles python environment setup failure', function()
+      vim.system = function(cmd)
+        if cmd[1] == 'ping' then
+          return {
+            wait = function()
+              return { code = 0 }
+            end,
+          }
+        elseif cmd[1] == 'uv' and cmd[2] == 'sync' then
+          return {
+            wait = function()
+              return { code = 1, stderr = 'setup failed' }
+            end,
+          }
+        end
+        return {
+          wait = function()
+            return { code = 0 }
+          end,
+        }
+      end
+
+      vim.fn.isdirectory = function()
+        return 0
+      end
+
+      local result = scrape.scrape_contest_metadata('atcoder', 'abc123')
+
+      assert.is_false(result.success)
+      assert.is_not_nil(result.error:match('Python environment setup failed'))
+    end)
+
+    it('handles network connectivity issues', function()
+      vim.system = function(cmd)
+        if cmd[1] == 'ping' then
+          return {
+            wait = function()
+              return { code = 1 }
+            end,
+          }
+        end
+        return {
+          wait = function()
+            return { code = 0 }
+          end,
+        }
+      end
+
+      local result = scrape.scrape_contest_metadata('atcoder', 'abc123')
+
+      assert.is_false(result.success)
+      assert.equals('No internet connection available', result.error)
+    end)
+  end)
+
+  describe('subprocess execution', function()
+    it('constructs correct command for atcoder metadata', function()
+      scrape.scrape_contest_metadata('atcoder', 'abc123')
+
+      local metadata_call = nil
+      for _, call in ipairs(mock_system_calls) do
+        if vim.tbl_contains(call.cmd, 'metadata') then
+          metadata_call = call
+          break
+        end
+      end
+
+      assert.is_not_nil(metadata_call)
+      assert.equals('uv', metadata_call.cmd[1])
+      assert.equals('run', metadata_call.cmd[2])
+      assert.is_true(vim.tbl_contains(metadata_call.cmd, 'metadata'))
+      assert.is_true(vim.tbl_contains(metadata_call.cmd, 'abc123'))
+    end)
+
+    it('constructs correct command for cses metadata', function()
+      scrape.scrape_contest_metadata('cses', 'problemset')
+
+      local metadata_call = nil
+      for _, call in ipairs(mock_system_calls) do
+        if vim.tbl_contains(call.cmd, 'metadata') then
+          metadata_call = call
+          break
+        end
+      end
+
+      assert.is_not_nil(metadata_call)
+      assert.equals('uv', metadata_call.cmd[1])
+      assert.is_true(vim.tbl_contains(metadata_call.cmd, 'metadata'))
+      assert.is_false(vim.tbl_contains(metadata_call.cmd, 'problemset'))
+    end)
+
+    it('handles subprocess execution failure', function()
+      vim.system = function(cmd)
+        if cmd[1] == 'ping' then
+          return {
+            wait = function()
+              return { code = 0 }
+            end,
+          }
+        elseif cmd[1] == 'uv' and vim.tbl_contains(cmd, 'metadata') then
+          return {
+            wait = function()
+              return { code = 1, stderr = 'execution failed' }
+            end,
+          }
+        end
+        return {
+          wait = function()
+            return { code = 0 }
+          end,
+        }
+      end
+
+      local result = scrape.scrape_contest_metadata('atcoder', 'abc123')
+
+      assert.is_false(result.success)
+      assert.is_not_nil(result.error:match('Failed to run metadata scraper'))
+      assert.is_not_nil(result.error:match('execution failed'))
+    end)
+  end)
+
+  describe('json parsing', function()
+    it('handles invalid json output', function()
+      vim.system = function(cmd)
+        if cmd[1] == 'ping' then
+          return {
+            wait = function()
+              return { code = 0 }
+            end,
+          }
+        elseif cmd[1] == 'uv' and vim.tbl_contains(cmd, 'metadata') then
+          return {
+            wait = function()
+              return { code = 0, stdout = 'invalid json' }
+            end,
+          }
+        end
+        return {
+          wait = function()
+            return { code = 0 }
+          end,
+        }
+      end
+
+      local result = scrape.scrape_contest_metadata('atcoder', 'abc123')
+
+      assert.is_false(result.success)
+      assert.is_not_nil(result.error:match('Failed to parse metadata scraper output'))
+    end)
+
+    it('handles scraper-reported failures', function()
+      vim.system = function(cmd)
+        if cmd[1] == 'ping' then
+          return {
+            wait = function()
+              return { code = 0 }
+            end,
+          }
+        elseif cmd[1] == 'uv' and vim.tbl_contains(cmd, 'metadata') then
+          return {
+            wait = function()
+              return {
+                code = 0,
+                stdout = '{"success": false, "error": "contest not found"}',
+              }
+            end,
+          }
+        end
+        return {
+          wait = function()
+            return { code = 0 }
+          end,
+        }
+      end
+
+      local result = scrape.scrape_contest_metadata('atcoder', 'abc123')
+
+      assert.is_false(result.success)
+      assert.equals('contest not found', result.error)
+    end)
+  end)
+
+  describe('problem scraping', function()
+    local test_context
+
+    before_each(function()
+      test_context = {
+        contest = 'atcoder',
+        contest_id = 'abc123',
+        problem_id = 'a',
+        problem_name = 'abc123a',
+        input_file = 'io/abc123a.cpin',
+        expected_file = 'io/abc123a.expected',
+      }
+    end)
+
+    it('uses existing files when available', function()
+      temp_files['io/abc123a.cpin'] = { '1 2' }
+      temp_files['io/abc123a.expected'] = { '3' }
+      temp_files['io/abc123a.1.cpin'] = { '4 5' }
+      temp_files['io/abc123a.1.cpout'] = { '9' }
+
+      local result = scrape.scrape_problem(test_context)
+
+      assert.is_true(result.success)
+      assert.equals('abc123a', result.problem_id)
+      assert.equals(1, result.test_count)
+      assert.equals(0, #mock_system_calls)
+    end)
+
+    it('scrapes and writes test case files', function()
+      local result = scrape.scrape_problem(test_context)
+
+      assert.is_true(result.success)
+      assert.equals('abc123a', result.problem_id)
+      assert.equals(1, result.test_count)
+      assert.is_not_nil(temp_files['io/abc123a.1.cpin'])
+      assert.is_not_nil(temp_files['io/abc123a.1.cpout'])
+      assert.equals('1 2', table.concat(temp_files['io/abc123a.1.cpin'], '\n'))
+      assert.equals('3', table.concat(temp_files['io/abc123a.1.cpout'], '\n'))
+    end)
+
+    it('constructs correct command for atcoder problem tests', function()
+      scrape.scrape_problem(test_context)
+
+      local tests_call = nil
+      for _, call in ipairs(mock_system_calls) do
+        if vim.tbl_contains(call.cmd, 'tests') then
+          tests_call = call
+          break
+        end
+      end
+
+      assert.is_not_nil(tests_call)
+      assert.is_true(vim.tbl_contains(tests_call.cmd, 'tests'))
+      assert.is_true(vim.tbl_contains(tests_call.cmd, 'abc123'))
+      assert.is_true(vim.tbl_contains(tests_call.cmd, 'a'))
+    end)
+
+    it('constructs correct command for cses problem tests', function()
+      test_context.contest = 'cses'
+      test_context.contest_id = '1001'
+      test_context.problem_id = nil
+
+      scrape.scrape_problem(test_context)
+
+      local tests_call = nil
+      for _, call in ipairs(mock_system_calls) do
+        if vim.tbl_contains(call.cmd, 'tests') then
+          tests_call = call
+          break
+        end
+      end
+
+      assert.is_not_nil(tests_call)
+      assert.is_true(vim.tbl_contains(tests_call.cmd, 'tests'))
+      assert.is_true(vim.tbl_contains(tests_call.cmd, '1001'))
+      assert.is_false(vim.tbl_contains(tests_call.cmd, 'a'))
+    end)
+  end)
+
+  describe('error scenarios', function()
+    it('validates input parameters', function()
+      assert.has_error(function()
+        scrape.scrape_contest_metadata(nil, 'abc123')
+      end)
+
+      assert.has_error(function()
+        scrape.scrape_contest_metadata('atcoder', nil)
+      end)
+    end)
+
+    it('handles file system errors gracefully', function()
+      vim.fn.mkdir = function()
+        error('permission denied')
+      end
+
+      local ctx = {
+        contest = 'atcoder',
+        contest_id = 'abc123',
+        problem_id = 'a',
+        problem_name = 'abc123a',
+        input_file = 'io/abc123a.cpin',
+        expected_file = 'io/abc123a.expected',
+      }
+
+      assert.has_error(function()
+        scrape.scrape_problem(ctx)
+      end)
+    end)
+  end)
+end)
diff --git a/spec/snippets_spec.lua b/spec/snippets_spec.lua
new file mode 100644
index 0000000..bdddb56
--- /dev/null
+++ b/spec/snippets_spec.lua
@@ -0,0 +1,215 @@
+describe('cp.snippets', function()
+  local snippets
+  local mock_luasnip
+
+  before_each(function()
+    snippets = require('cp.snippets')
+    mock_luasnip = {
+      snippet = function(trigger, body)
+        return { trigger = trigger, body = body }
+      end,
+      insert_node = function(pos)
+        return { type = 'insert', pos = pos }
+      end,
+      add_snippets = function(filetype, snippet_list)
+        mock_luasnip.added = mock_luasnip.added or {}
+        mock_luasnip.added[filetype] = snippet_list
+      end,
+      added = {},
+    }
+
+    mock_luasnip.extras = {
+      fmt = {
+        fmt = function(template, nodes)
+          return { template = template, nodes = nodes }
+        end,
+      },
+    }
+
+    package.loaded['luasnip'] = mock_luasnip
+    package.loaded['luasnip.extras.fmt'] = mock_luasnip.extras.fmt
+  end)
+
+  after_each(function()
+    package.loaded['luasnip'] = nil
+    package.loaded['luasnip.extras.fmt'] = nil
+  end)
+
+  describe('setup without luasnip', function()
+    it('handles missing luasnip gracefully', function()
+      package.loaded['luasnip'] = nil
+
+      assert.has_no_errors(function()
+        snippets.setup({})
+      end)
+    end)
+  end)
+
+  describe('setup with luasnip available', function()
+    it('sets up default cpp snippets for all contests', function()
+      local config = { snippets = {} }
+
+      snippets.setup(config)
+
+      assert.is_not_nil(mock_luasnip.added.cpp)
+      assert.is_true(#mock_luasnip.added.cpp >= 3)
+
+      local triggers = {}
+      for _, snippet in ipairs(mock_luasnip.added.cpp) do
+        table.insert(triggers, snippet.trigger)
+      end
+
+      assert.is_true(vim.tbl_contains(triggers, 'cp.nvim/codeforces.cpp'))
+      assert.is_true(vim.tbl_contains(triggers, 'cp.nvim/atcoder.cpp'))
+      assert.is_true(vim.tbl_contains(triggers, 'cp.nvim/cses.cpp'))
+    end)
+
+    it('sets up default python snippets for all contests', function()
+      local config = { snippets = {} }
+
+      snippets.setup(config)
+
+      assert.is_not_nil(mock_luasnip.added.python)
+      assert.is_true(#mock_luasnip.added.python >= 3)
+
+      local triggers = {}
+      for _, snippet in ipairs(mock_luasnip.added.python) do
+        table.insert(triggers, snippet.trigger)
+      end
+
+      assert.is_true(vim.tbl_contains(triggers, 'cp.nvim/codeforces.python'))
+      assert.is_true(vim.tbl_contains(triggers, 'cp.nvim/atcoder.python'))
+      assert.is_true(vim.tbl_contains(triggers, 'cp.nvim/cses.python'))
+    end)
+
+    it('includes template content with placeholders', function()
+      local config = { snippets = {} }
+
+      snippets.setup(config)
+
+      local cpp_snippets = mock_luasnip.added.cpp or {}
+      local codeforces_snippet = nil
+      for _, snippet in ipairs(cpp_snippets) do
+        if snippet.trigger == 'cp.nvim/codeforces.cpp' then
+          codeforces_snippet = snippet
+          break
+        end
+      end
+
+      assert.is_not_nil(codeforces_snippet)
+      assert.is_not_nil(codeforces_snippet.body)
+      assert.equals('table', type(codeforces_snippet.body))
+      assert.is_not_nil(codeforces_snippet.body.template:match('#include'))
+      assert.is_not_nil(codeforces_snippet.body.template:match('void solve'))
+    end)
+
+    it('respects user snippet overrides', function()
+      local custom_snippet = {
+        trigger = 'cp.nvim/custom.cpp',
+        body = 'custom template',
+      }
+      local config = {
+        snippets = { custom_snippet },
+      }
+
+      snippets.setup(config)
+
+      local cpp_snippets = mock_luasnip.added.cpp or {}
+      local found_custom = false
+      for _, snippet in ipairs(cpp_snippets) do
+        if snippet.trigger == 'cp.nvim/custom.cpp' then
+          found_custom = true
+          assert.equals('custom template', snippet.body)
+          break
+        end
+      end
+      assert.is_true(found_custom)
+    end)
+
+    it('filters user snippets by language', function()
+      local cpp_snippet = {
+        trigger = 'cp.nvim/custom.cpp',
+        body = 'cpp template',
+      }
+      local python_snippet = {
+        trigger = 'cp.nvim/custom.python',
+        body = 'python template',
+      }
+      local config = {
+        snippets = { cpp_snippet, python_snippet },
+      }
+
+      snippets.setup(config)
+
+      local cpp_snippets = mock_luasnip.added.cpp or {}
+      local python_snippets = mock_luasnip.added.python or {}
+
+      local cpp_has_custom = false
+      for _, snippet in ipairs(cpp_snippets) do
+        if snippet.trigger == 'cp.nvim/custom.cpp' then
+          cpp_has_custom = true
+          break
+        end
+      end
+
+      local python_has_custom = false
+      for _, snippet in ipairs(python_snippets) do
+        if snippet.trigger == 'cp.nvim/custom.python' then
+          python_has_custom = true
+          break
+        end
+      end
+
+      assert.is_true(cpp_has_custom)
+      assert.is_true(python_has_custom)
+    end)
+
+    it('handles empty config gracefully', function()
+      assert.has_no_errors(function()
+        snippets.setup({})
+      end)
+
+      assert.is_not_nil(mock_luasnip.added.cpp)
+      assert.is_not_nil(mock_luasnip.added.python)
+    end)
+
+    it('handles empty config gracefully', function()
+      assert.has_no_errors(function()
+        snippets.setup({ snippets = {} })
+      end)
+    end)
+
+    it('creates templates for correct filetypes', function()
+      local config = { snippets = {} }
+
+      snippets.setup(config)
+
+      assert.is_not_nil(mock_luasnip.added.cpp)
+      assert.is_not_nil(mock_luasnip.added.python)
+      assert.is_nil(mock_luasnip.added.c)
+      assert.is_nil(mock_luasnip.added.py)
+    end)
+
+    it('excludes overridden default snippets', function()
+      local override_snippet = {
+        trigger = 'cp.nvim/codeforces.cpp',
+        body = 'overridden template',
+      }
+      local config = {
+        snippets = { override_snippet },
+      }
+
+      snippets.setup(config)
+
+      local cpp_snippets = mock_luasnip.added.cpp or {}
+      local codeforces_count = 0
+      for _, snippet in ipairs(cpp_snippets) do
+        if snippet.trigger == 'cp.nvim/codeforces.cpp' then
+          codeforces_count = codeforces_count + 1
+        end
+      end
+
+      assert.equals(1, codeforces_count)
+    end)
+  end)
+end)