diff --git a/tests/test_generator.py b/tests/test_generator.py
new file mode 100644
index 0000000..2750cbb
--- /dev/null
+++ b/tests/test_generator.py
@@ -0,0 +1,240 @@
+"""Tests for commit message generator."""
+
+from unittest.mock import patch
+
+import pytest
+
+from src.analyzer import ChangeSet, ChangeType, StagedChange
+from src.generator import (
+    GenerationError,
+    detect_commit_type,
+    detect_scope,
+    generate_commit_message,
+    generate_description,
+)
+
+
+class TestDetectCommitType:
+    """Tests for commit type detection."""
+
+    def test_detects_feat_for_src_files(self):
+        """Test detecting 'feat' for source files."""
+        change_set = ChangeSet([
+            StagedChange("src/main.py", ChangeType.ADDED),
+            StagedChange("src/cli.py", ChangeType.MODIFIED),
+        ])
+        result = detect_commit_type(change_set)
+        assert result == "feat"
+
+    def test_detects_fix_for_bug_fixes(self):
+        """Test detecting 'fix' for bug-related changes."""
+        change_set = ChangeSet([
+            StagedChange("bug_fix.py", ChangeType.MODIFIED),
+            StagedChange("fix_login.py", ChangeType.MODIFIED),
+        ])
+        result = detect_commit_type(change_set)
+        assert result == "fix"
+
+    def test_detects_docs_for_markdown(self):
+        """Test detecting 'docs' for markdown files."""
+        change_set = ChangeSet([
+            StagedChange("README.md", ChangeType.MODIFIED),
+            StagedChange("docs/guide.md", ChangeType.ADDED),
+        ])
+        result = detect_commit_type(change_set)
+        assert result == "docs"
+
+    def test_detects_test_for_test_files(self):
+        """Test detecting 'test' for test files."""
+        change_set = ChangeSet([
+            StagedChange("tests/test_main.py", ChangeType.ADDED),
+            StagedChange("test_main.spec.js", ChangeType.MODIFIED),
+        ])
+        result = detect_commit_type(change_set)
+        assert result == "test"
+
+    def test_detects_chore_for_config(self):
+        """Test detecting 'chore' for configuration files."""
+        change_set = ChangeSet([
+            StagedChange("package.json", ChangeType.MODIFIED),
+            StagedChange(".gitignore", ChangeType.ADDED),
+        ])
+        result = detect_commit_type(change_set)
+        assert result == "chore"
+
+    def test_falls_back_to_chore(self):
+        """Test falling back to 'chore' when no pattern matches."""
+        change_set = ChangeSet([
+            StagedChange("unknown/file.xyz", ChangeType.ADDED),
+        ])
+        result = detect_commit_type(change_set)
+        assert result == "chore"
+
+    def test_custom_type_rules(self):
+        """Test using custom type rules."""
+        change_set = ChangeSet([
+            StagedChange("custom/feature.py", ChangeType.ADDED),
+        ])
+        custom_rules = {"custom_type": ["custom/"]}
+        result = detect_commit_type(change_set, custom_rules)
+        assert result == "custom_type"
+
+
+class TestDetectScope:
+    """Tests for scope detection."""
+
+    def test_detects_single_scope(self):
+        """Test detecting single scope from directory."""
+        change_set = ChangeSet([
+            StagedChange("src/cli/main.py", ChangeType.ADDED),
+            StagedChange("src/cli/commands.py", ChangeType.MODIFIED),
+        ])
+        result = detect_scope(change_set)
+        assert result == "src"
+
+    def test_detects_multiple_scopes(self):
+        """Test detecting multiple scopes."""
+        change_set = ChangeSet([
+            StagedChange("src/a.py", ChangeType.ADDED),
+            StagedChange("lib/b.py", ChangeType.MODIFIED),
+        ])
+        result = detect_scope(change_set)
+        assert "src" in result and "lib" in result
+
+    def test_empty_for_no_changes(self):
+        """Test returning empty string for no changes."""
+        change_set = ChangeSet([])
+        result = detect_scope(change_set)
+        assert result == ""
+
+    def test_root_file_no_scope(self):
+        """Test no scope for root-level files."""
+        change_set = ChangeSet([
+            StagedChange("main.py", ChangeType.ADDED),
+        ])
+        result = detect_scope(change_set)
+        assert result == ""
+
+
+class TestGenerateDescription:
+    """Tests for description generation."""
+
+    def test_describes_single_added(self):
+        """Test generating description for single added file."""
+        change_set = ChangeSet([
+            StagedChange("new_file.py", ChangeType.ADDED),
+        ])
+        result = generate_description(change_set)
+        assert result == "add new_file.py"
+
+    def test_describes_single_deleted(self):
+        """Test generating description for deleted file."""
+        change_set = ChangeSet([
+            StagedChange("old_file.py", ChangeType.DELETED),
+        ])
+        result = generate_description(change_set)
+        assert result == "remove old_file.py"
+
+    def test_describes_single_modified(self):
+        """Test generating description for modified file."""
+        change_set = ChangeSet([
+            StagedChange("existing.py", ChangeType.MODIFIED),
+        ])
+        result = generate_description(change_set)
+        assert result == "update existing.py"
+
+    def test_describes_multiple_added(self):
+        """Test generating description for multiple added files."""
+        change_set = ChangeSet([
+            StagedChange("a.py", ChangeType.ADDED),
+            StagedChange("b.py", ChangeType.ADDED),
+        ])
+        result = generate_description(change_set)
+        assert result == "add 2 files"
+
+    def test_describes_multiple_modified(self):
+        """Test generating description for multiple modified files."""
+        change_set = ChangeSet([
+            StagedChange("a.py", ChangeType.MODIFIED),
+            StagedChange("b.py", ChangeType.MODIFIED),
+        ])
+        result = generate_description(change_set)
+        assert result == "update 2 files"
+
+    def test_default_for_empty(self):
+        """Test default description for empty change set."""
+        change_set = ChangeSet([])
+        result = generate_description(change_set)
+        assert result == "update"
+
+
+class TestGenerateCommitMessage:
+    """Tests for full message generation."""
+
+    @patch("src.generator.ChangeAnalyzer")
+    def test_generates_valid_message(self, mock_analyzer):
+        """Test generating a complete commit message."""
+        change_set = ChangeSet([
+            StagedChange("src/main.py", ChangeType.ADDED),
+        ])
+        mock_analyzer.return_value.get_staged_changes.return_value = change_set
+
+        result = generate_commit_message()
+
+        assert "feat" in result
+        assert "src" in result
+
+    def test_raises_error_on_no_changes(self):
+        """Test raising error when no staged changes."""
+        with patch("src.generator.ChangeAnalyzer") as mock_analyzer:
+            mock_analyzer.return_value.get_staged_changes.return_value = ChangeSet([])
+
+            with pytest.raises(GenerationError, match="No staged changes"):
+                generate_commit_message()
+
+    def test_raises_error_on_invalid_repo(self):
+        """Test raising error for invalid repository."""
+        with patch("src.generator.ChangeAnalyzer") as mock_analyzer:
+            mock_analyzer.return_value.get_staged_changes.side_effect = ValueError(
+                "Not a git repository"
+            )
+
+            with pytest.raises(GenerationError, match="Not a git repository"):
+                generate_commit_message()
+
+    @patch("src.generator.ChangeAnalyzer")
+    def test_respects_config_template(self, mock_analyzer):
+        """Test using custom template from config."""
+        change_set = ChangeSet([
+            StagedChange("src/test.py", ChangeType.ADDED),
+        ])
+        custom_config = {"template": "CUSTOM: {description}"}
+
+        mock_analyzer.return_value.get_staged_changes.return_value = change_set
+
+        with patch("src.generator.load_config") as mock_load_config:
+            mock_load_config.return_value = custom_config
+
+            result = generate_commit_message()
+
+            assert result.startswith("CUSTOM:")
+
+    @patch("src.generator.ChangeAnalyzer")
+    def test_max_files_limit(self, mock_analyzer):
+        """Test respecting max files configuration."""
+        changes = [StagedChange(f"file{i}.py", ChangeType.ADDED) for i in range(10)]
+        change_set = ChangeSet(changes)
+        custom_config = {
+            "include_file_list": True,
+            "max_files": 3,
+            "template": "{files}"
+        }
+
+        mock_analyzer.return_value.get_staged_changes.return_value = change_set
+
+        with patch("src.generator.load_config") as mock_load_config:
+            mock_load_config.return_value = custom_config
+
+            result = generate_commit_message()
+            file_count = result.count("file")
+            assert file_count <= 3