test: add store, parse, and diff specs

Problem: need test coverage for core data operations, inline
metadata parsing, and buffer diff algorithm.

Solution: add busted specs for store CRUD, round-trip
preservation, parse body/command_add with configurable date
syntax, and diff create/delete/update/copy/move operations.

spec/parse_spec.lua

@@ -0,0 +1,117 @@
+require('spec.helpers')
+
+local config = require('todo.config')
+
+describe('parse', function()
+  before_each(function()
+    vim.g.todo = nil
+    config.reset()
+  end)
+
+  after_each(function()
+    vim.g.todo = nil
+    config.reset()
+  end)
+
+  local parse = require('todo.parse')
+
+  describe('body', function()
+    it('returns plain description when no metadata', function()
+      local desc, meta = parse.body('Buy groceries')
+      assert.are.equal('Buy groceries', desc)
+      assert.are.same({}, meta)
+    end)
+
+    it('extracts due date', function()
+      local desc, meta = parse.body('Buy groceries due:2026-03-15')
+      assert.are.equal('Buy groceries', desc)
+      assert.are.equal('2026-03-15', meta.due)
+    end)
+
+    it('extracts category', function()
+      local desc, meta = parse.body('Buy groceries cat:Errands')
+      assert.are.equal('Buy groceries', desc)
+      assert.are.equal('Errands', meta.cat)
+    end)
+
+    it('extracts both due and cat', function()
+      local desc, meta = parse.body('Buy milk due:2026-03-15 cat:Errands')
+      assert.are.equal('Buy milk', desc)
+      assert.are.equal('2026-03-15', meta.due)
+      assert.are.equal('Errands', meta.cat)
+    end)
+
+    it('extracts metadata in any order', function()
+      local desc, meta = parse.body('Buy milk cat:Errands due:2026-03-15')
+      assert.are.equal('Buy milk', desc)
+      assert.are.equal('2026-03-15', meta.due)
+      assert.are.equal('Errands', meta.cat)
+    end)
+
+    it('stops at duplicate key', function()
+      local desc, meta = parse.body('Buy milk due:2026-03-15 due:2026-04-01')
+      assert.are.equal('Buy milk due:2026-03-15', desc)
+      assert.are.equal('2026-04-01', meta.due)
+    end)
+
+    it('stops at non-meta token', function()
+      local desc, meta = parse.body('Buy milk for breakfast due:2026-03-15')
+      assert.are.equal('Buy milk for breakfast', desc)
+      assert.are.equal('2026-03-15', meta.due)
+    end)
+
+    it('rejects invalid dates', function()
+      local desc, meta = parse.body('Buy milk due:2026-13-15')
+      assert.are.equal('Buy milk due:2026-13-15', desc)
+      assert.is_nil(meta.due)
+    end)
+
+    it('preserves colons in description', function()
+      local desc, meta = parse.body('Meeting at 3:00pm')
+      assert.are.equal('Meeting at 3:00pm', desc)
+      assert.are.same({}, meta)
+    end)
+
+    it('uses configurable date syntax', function()
+      vim.g.todo = { date_syntax = 'by' }
+      config.reset()
+      local desc, meta = parse.body('Buy milk by:2026-03-15')
+      assert.are.equal('Buy milk', desc)
+      assert.are.equal('2026-03-15', meta.due)
+    end)
+
+    it('ignores old syntax when date_syntax is changed', function()
+      vim.g.todo = { date_syntax = 'by' }
+      config.reset()
+      local desc, meta = parse.body('Buy milk due:2026-03-15')
+      assert.are.equal('Buy milk due:2026-03-15', desc)
+      assert.is_nil(meta.due)
+    end)
+  end)
+
+  describe('command_add', function()
+    it('parses simple text', function()
+      local desc, meta = parse.command_add('Buy milk')
+      assert.are.equal('Buy milk', desc)
+      assert.are.same({}, meta)
+    end)
+
+    it('detects category prefix', function()
+      local desc, meta = parse.command_add('School: Do homework')
+      assert.are.equal('Do homework', desc)
+      assert.are.equal('School', meta.cat)
+    end)
+
+    it('ignores lowercase prefix', function()
+      local desc, meta = parse.command_add('hello: world')
+      assert.are.equal('hello: world', desc)
+    end)
+
+    it('combines category prefix with inline metadata', function()
+      local desc, meta = parse.command_add('School: Do homework due:2026-03-15')
+      assert.are.equal('Do homework', desc)
+      assert.are.equal('School', meta.cat)
+      assert.are.equal('2026-03-15', meta.due)
+    end)
+  end)
+end)