feat: some more tests, a checkpoint

spec/highlight_spec.lua

@@ -0,0 +1,39 @@
+describe('cp.highlight', function()
+  local highlight = require('cp.highlight')
+
+  describe('parse_diff_line', function()
+    it('parses added text markers {+text+}')
+    it('removes removed text markers [-text-]')
+    it('handles mixed add/remove markers')
+    it('calculates correct highlight positions')
+    it('handles text without markers')
+    it('handles empty text')
+  end)
+
+  describe('parse_git_diff', function()
+    it('skips git diff headers')
+    it('processes added lines')
+    it('ignores removed lines')
+    it('handles unchanged lines')
+    it('sets correct line numbers')
+    it('handles empty diff output')
+  end)
+
+  describe('apply_highlights', function()
+    it('clears existing highlights')
+    it('applies extmarks with correct positions')
+    it('uses correct highlight groups')
+    it('handles empty highlights')
+  end)
+
+  describe('create_namespace', function()
+    it('creates unique namespace')
+  end)
+
+  describe('parse_and_apply_diff', function()
+    it('parses diff and applies to buffer')
+    it('sets buffer content')
+    it('applies highlights')
+    it('returns content lines')
+  end)
+end)