diff --git a/app/tests/test_message_generator.py b/app/tests/test_message_generator.py
new file mode 100644
index 0000000..85d0a8c
--- /dev/null
+++ b/app/tests/test_message_generator.py
@@ -0,0 +1,133 @@
+"""Tests for message_generator.py."""
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from git_commit_generator.message_generator import MessageGenerator
+
+
+class TestMessageGenerator:
+    """Test cases for MessageGenerator."""
+
+    @pytest.fixture
+    def message_generator(self):
+        """Create a MessageGenerator instance with mocked dependencies."""
+        with patch("git_commit_generator.message_generator.get_config") as mock_config:
+            with patch("git_commit_generator.message_generator.get_ollama_client") as mock_ollama:
+                config = MagicMock()
+                config.ollama_host = "http://localhost:11434"
+                config.ollama_model = "llama3"
+                config.read_prompt.return_value = "Generate a commit message."
+                mock_config.return_value = config
+
+                ollama_client = MagicMock()
+                ollama_client.generate_commit_message.return_value = "feat(core): test feature"
+                mock_ollama.return_value = ollama_client
+
+                with patch("git_commit_generator.message_generator.get_git_utils") as mock_git:
+                    git_utils = MagicMock()
+                    git_utils.get_all_changes.return_value = "diff content"
+                    mock_git.return_value = git_utils
+
+                    generator = MessageGenerator(
+                        config=config,
+                        ollama_client=ollama_client,
+                    )
+                    generator.git_utils = git_utils
+                    yield generator
+
+    def test_detect_change_type_feature(self, message_generator):
+        """Test change type detection for features."""
+        diff = "+def new_function():\n    return 'hello'"
+        result = message_generator.detect_change_type(diff)
+        assert result == "feat"
+
+    def test_detect_change_type_fix(self, message_generator):
+        """Test change type detection for fixes."""
+        diff = "-def old_function():\n    bug fix"
+        result = message_generator.detect_change_type(diff)
+        assert result == "fix"
+
+    def test_detect_change_type_test(self, message_generator):
+        """Test change type detection for tests."""
+        diff = "+def test_function():\n    assert True"
+        result = message_generator.detect_change_type(diff)
+        assert result == "test"
+
+    def test_detect_change_type_docs(self, message_generator):
+        """Test change type detection for documentation."""
+        diff = "update readme documentation"
+        result = message_generator.detect_change_type(diff)
+        assert result == "docs"
+
+    def test_detect_scope_files(self, message_generator):
+        """Test scope detection from file paths."""
+        files = ["api/main.py", "api/routes.py"]
+        result = message_generator.detect_scope(files)
+        assert result == "api"
+
+    def test_detect_scope_root_files(self, message_generator):
+        """Test scope detection for root files."""
+        files = ["main.py", "config.py"]
+        result = message_generator.detect_scope(files)
+        assert result == "core"
+
+    def test_parse_conventional_message_full(self, message_generator):
+        """Test parsing a full conventional commit message."""
+        message = "feat(auth): add login functionality"
+        result = message_generator.parse_conventional_message(message)
+        assert result["type"] == "feat"
+        assert result["scope"] == "auth"
+        assert result["description"] == "add login functionality"
+        assert result["full_message"] == message
+
+    def test_parse_conventional_message_no_scope(self, message_generator):
+        """Test parsing a conventional message without scope."""
+        message = "fix: resolve memory leak"
+        result = message_generator.parse_conventional_message(message)
+        assert result["type"] == "fix"
+        assert result["scope"] == ""
+        assert result["description"] == "resolve memory leak"
+
+    def test_format_conventional_message_with_scope(self, message_generator):
+        """Test formatting a message with scope."""
+        message = message_generator.format_conventional_message(
+            message_type="feat",
+            scope="api",
+            description="add new endpoint"
+        )
+        assert message == "feat(api): add new endpoint"
+
+    def test_format_conventional_message_no_scope(self, message_generator):
+        """Test formatting a message without scope."""
+        message = message_generator.format_conventional_message(
+            message_type="fix",
+            scope="",
+            description="fix bug"
+        )
+        assert message == "fix: fix bug"
+
+    def test_clean_message_removes_quotes(self, message_generator):
+        """Test that clean_message removes surrounding quotes."""
+        message = '"feat(core): test message"'
+        result = message_generator._clean_message(message)
+        assert result == "feat(core): test message"
+
+    def test_clean_message_strips_whitespace(self, message_generator):
+        """Test that clean_message strips whitespace."""
+        message = "  feat(core): test message  \n"
+        result = message_generator._clean_message(message)
+        assert result == "feat(core): test message"
+
+    def test_generate_success(self, message_generator):
+        """Test successful message generation."""
+        with patch.object(message_generator, 'ollama_client') as mock_client:
+            mock_client.generate_commit_message.return_value = "feat(core): test"
+            result = message_generator.generate()
+            assert result == "feat(core): test"
+
+    def test_generate_no_changes_raises_error(self, message_generator):
+        """Test that generate raises error when no changes."""
+        message_generator.git_utils.get_all_changes.return_value = ""
+        with pytest.raises(ValueError, match="No changes detected"):
+            message_generator.generate()