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/store_spec.lua

@@ -0,0 +1,189 @@
+require('spec.helpers')
+
+local config = require('todo.config')
+local store = require('todo.store')
+
+describe('store', function()
+  local tmpdir
+
+  before_each(function()
+    tmpdir = vim.fn.tempname()
+    vim.fn.mkdir(tmpdir, 'p')
+    vim.g.todo = { data_path = tmpdir .. '/tasks.json' }
+    config.reset()
+    store.unload()
+  end)
+
+  after_each(function()
+    vim.fn.delete(tmpdir, 'rf')
+    vim.g.todo = nil
+    config.reset()
+  end)
+
+  describe('load', function()
+    it('returns empty data when no file exists', function()
+      local data = store.load()
+      assert.are.equal(1, data.version)
+      assert.are.equal(1, data.next_id)
+      assert.are.same({}, data.tasks)
+    end)
+
+    it('loads existing data', function()
+      local path = config.get().data_path
+      local f = io.open(path, 'w')
+      f:write(vim.json.encode({
+        version = 1,
+        next_id = 3,
+        tasks = {
+          {
+            id = 1,
+            description = 'Todo one',
+            status = 'pending',
+            entry = '2026-01-01T00:00:00Z',
+            modified = '2026-01-01T00:00:00Z',
+          },
+          {
+            id = 2,
+            description = 'Todo two',
+            status = 'done',
+            entry = '2026-01-01T00:00:00Z',
+            modified = '2026-01-01T00:00:00Z',
+          },
+        },
+      }))
+      f:close()
+      local data = store.load()
+      assert.are.equal(3, data.next_id)
+      assert.are.equal(2, #data.tasks)
+      assert.are.equal('Todo one', data.tasks[1].description)
+      assert.are.equal('done', data.tasks[2].status)
+    end)
+
+    it('preserves unknown fields', function()
+      local path = config.get().data_path
+      local f = io.open(path, 'w')
+      f:write(vim.json.encode({
+        version = 1,
+        next_id = 2,
+        tasks = {
+          {
+            id = 1,
+            description = 'Todo',
+            status = 'pending',
+            entry = '2026-01-01T00:00:00Z',
+            modified = '2026-01-01T00:00:00Z',
+            custom_field = 'hello',
+          },
+        },
+      }))
+      f:close()
+      store.load()
+      local task = store.get(1)
+      assert.is_not_nil(task._extra)
+      assert.are.equal('hello', task._extra.custom_field)
+    end)
+  end)
+
+  describe('add', function()
+    it('creates a task with incremented id', function()
+      store.load()
+      local t1 = store.add({ description = 'First' })
+      local t2 = store.add({ description = 'Second' })
+      assert.are.equal(1, t1.id)
+      assert.are.equal(2, t2.id)
+      assert.are.equal('pending', t1.status)
+      assert.are.equal('Inbox', t1.category)
+    end)
+
+    it('uses provided category', function()
+      store.load()
+      local t = store.add({ description = 'Test', category = 'Work' })
+      assert.are.equal('Work', t.category)
+    end)
+  end)
+
+  describe('update', function()
+    it('updates fields and sets modified', function()
+      store.load()
+      local t = store.add({ description = 'Original' })
+      local original_modified = t.modified
+      store.update(t.id, { description = 'Updated' })
+      local updated = store.get(t.id)
+      assert.are.equal('Updated', updated.description)
+      assert.is_not.equal(original_modified, updated.modified)
+    end)
+
+    it('sets end timestamp on completion', function()
+      store.load()
+      local t = store.add({ description = 'Test' })
+      assert.is_nil(t['end'])
+      store.update(t.id, { status = 'done' })
+      local updated = store.get(t.id)
+      assert.is_not_nil(updated['end'])
+    end)
+  end)
+
+  describe('delete', function()
+    it('marks task as deleted', function()
+      store.load()
+      local t = store.add({ description = 'To delete' })
+      store.delete(t.id)
+      local deleted = store.get(t.id)
+      assert.are.equal('deleted', deleted.status)
+      assert.is_not_nil(deleted['end'])
+    end)
+  end)
+
+  describe('save and round-trip', function()
+    it('persists and reloads correctly', function()
+      store.load()
+      store.add({ description = 'Persisted', category = 'Work', priority = 1 })
+      store.save()
+      store.unload()
+      store.load()
+      local tasks = store.active_tasks()
+      assert.are.equal(1, #tasks)
+      assert.are.equal('Persisted', tasks[1].description)
+      assert.are.equal('Work', tasks[1].category)
+      assert.are.equal(1, tasks[1].priority)
+    end)
+
+    it('round-trips unknown fields', function()
+      local path = config.get().data_path
+      local f = io.open(path, 'w')
+      f:write(vim.json.encode({
+        version = 1,
+        next_id = 2,
+        tasks = {
+          {
+            id = 1,
+            description = 'Todo',
+            status = 'pending',
+            entry = '2026-01-01T00:00:00Z',
+            modified = '2026-01-01T00:00:00Z',
+            _gcal_event_id = 'abc123',
+          },
+        },
+      }))
+      f:close()
+      store.load()
+      store.save()
+      store.unload()
+      store.load()
+      local task = store.get(1)
+      assert.are.equal('abc123', task._extra._gcal_event_id)
+    end)
+  end)
+
+  describe('active_tasks', function()
+    it('excludes deleted tasks', function()
+      store.load()
+      store.add({ description = 'Active' })
+      local t2 = store.add({ description = 'To delete' })
+      store.delete(t2.id)
+      local active = store.active_tasks()
+      assert.are.equal(1, #active)
+      assert.are.equal('Active', active[1].description)
+    end)
+  end)
+end)