diff --git a/.tests/unit/test_cli.py b/.tests/unit/test_cli.py
new file mode 100644
index 0000000..a4d361a
--- /dev/null
+++ b/.tests/unit/test_cli.py
@@ -0,0 +1,82 @@
+"""Unit tests for CLI interface."""
+
+import pytest
+import os
+from click.testing import CliRunner
+from code_doc_cli.cli.main import cli, ExitCode
+
+
+class TestCLI:
+    """Tests for CLI commands."""
+
+    @pytest.fixture
+    def runner(self):
+        return CliRunner()
+
+    def test_version_command(self, runner):
+        """Test version command."""
+        result = runner.invoke(cli, ["version"])
+        assert result.exit_code == 0
+        assert "version" in result.output.lower()
+
+    def test_languages_command(self, runner):
+        """Test languages command."""
+        result = runner.invoke(cli, ["languages"])
+        assert result.exit_code == 0
+        assert "python" in result.output
+        assert "typescript" in result.output
+        assert "go" in result.output
+
+    def test_init_command(self, runner):
+        """Test init command."""
+        with runner.isolated_filesystem():
+            result = runner.invoke(cli, ["init"], input="y\n")
+            assert result.exit_code == 0
+            assert "code-doc.toml" in result.output
+
+    def test_generate_no_files_error(self, runner):
+        """Test generate with no files."""
+        with runner.isolated_filesystem():
+            result = runner.invoke(cli, ["generate"])
+            assert result.exit_code == ExitCode.NO_FILES
+            assert "No source files" in result.output
+
+    def test_generate_python_file(self, runner):
+        """Test generate with Python file."""
+        with runner.isolated_filesystem():
+            with open("test.py", "w") as f:
+                f.write('''
+def add(a: int, b: int) -> int:
+    """Add two numbers."""
+    return a + b
+''')
+            result = runner.invoke(cli, ["generate", "test.py"])
+            assert result.exit_code == 0
+            assert "API Documentation" in result.output
+            assert "add" in result.output
+
+
+class TestExitCodes:
+    """Tests for exit codes."""
+
+    @pytest.fixture
+    def runner(self):
+        return CliRunner()
+
+    def test_success_exit_code(self, runner):
+        """Test successful execution returns 0."""
+        with runner.isolated_filesystem():
+            with open("test.py", "w") as f:
+                f.write('''
+def add(a: int, b: int) -> int:
+    """Add two numbers."""
+    return a + b
+''')
+            result = runner.invoke(cli, ["generate", "test.py"])
+            assert result.exit_code == ExitCode.SUCCESS
+
+    def test_no_files_exit_code(self, runner):
+        """Test no files found returns 1."""
+        with runner.isolated_filesystem():
+            result = runner.invoke(cli, ["generate"])
+            assert result.exit_code == ExitCode.NO_FILES