diff --git a/tests/test_cli.py b/tests/test_cli.py
new file mode 100644
index 0000000..715901e
--- /dev/null
+++ b/tests/test_cli.py
@@ -0,0 +1,194 @@
+"""Tests for CLI module."""
+
+import pytest
+from typer.testing import CliRunner
+
+from src.cli.commands import app
+from src.cli.options import OutputFormat, SeverityLevel, LanguageType, resolve_output_format, resolve_severity, resolve_language
+
+
+class TestCLIOptions:
+    """Tests for CLI options and enums."""
+
+    def test_output_format_enum_values(self):
+        """Test OutputFormat enum values."""
+        assert OutputFormat.TERMINAL.value == "terminal"
+        assert OutputFormat.JSON.value == "json"
+        assert OutputFormat.MARKDOWN.value == "markdown"
+
+    def test_severity_level_enum_values(self):
+        """Test SeverityLevel enum values."""
+        assert SeverityLevel.LOW.value == "low"
+        assert SeverityLevel.MEDIUM.value == "medium"
+        assert SeverityLevel.HIGH.value == "high"
+        assert SeverityLevel.CRITICAL.value == "critical"
+
+    def test_language_type_enum_values(self):
+        """Test LanguageType enum values."""
+        assert LanguageType.PYTHON.value == "python"
+        assert LanguageType.JAVASCRIPT.value == "javascript"
+        assert LanguageType.TYPESCRIPT.value == "typescript"
+
+    def test_resolve_output_format_terminal(self):
+        """Test resolving terminal format."""
+        assert resolve_output_format("terminal") == OutputFormat.TERMINAL
+        assert resolve_output_format("TERMINAL") == OutputFormat.TERMINAL
+        assert resolve_output_format(None) == OutputFormat.TERMINAL
+
+    def test_resolve_output_format_json(self):
+        """Test resolving JSON format."""
+        assert resolve_output_format("json") == OutputFormat.JSON
+        assert resolve_output_format("JSON") == OutputFormat.JSON
+
+    def test_resolve_output_format_markdown(self):
+        """Test resolving Markdown format."""
+        assert resolve_output_format("markdown") == OutputFormat.MARKDOWN
+        assert resolve_output_format("MARKDOWN") == OutputFormat.MARKDOWN
+
+    def test_resolve_output_format_invalid(self):
+        """Test resolving invalid format returns terminal."""
+        assert resolve_output_format("invalid") == OutputFormat.TERMINAL
+
+    def test_resolve_severity(self):
+        """Test resolving severity levels."""
+        assert resolve_severity("low") == SeverityLevel.LOW
+        assert resolve_severity("medium") == SeverityLevel.MEDIUM
+        assert resolve_severity("high") == SeverityLevel.HIGH
+        assert resolve_severity("critical") == SeverityLevel.CRITICAL
+        assert resolve_severity("MEDIUM") == SeverityLevel.MEDIUM
+        assert resolve_severity(None) is None
+        assert resolve_severity("invalid") is None
+
+    def test_resolve_language(self):
+        """Test resolving language types."""
+        assert resolve_language("python") == LanguageType.PYTHON
+        assert resolve_language("javascript") == LanguageType.JAVASCRIPT
+        assert resolve_language("typescript") == LanguageType.TYPESCRIPT
+        assert resolve_language("PYTHON") == LanguageType.PYTHON
+        assert resolve_language(None) is None
+        assert resolve_language("invalid") is None
+
+
+class TestCLIScanCommand:
+    """Tests for CLI scan command."""
+
+    @pytest.fixture
+    def runner(self):
+        """Create CLI runner."""
+        return CliRunner()
+
+    def test_scan_command_help(self, runner):
+        """Test scan command help output."""
+        result = runner.invoke(app, ["scan", "--help"])
+        assert result.exit_code == 0
+        assert "Scan code for issues" in result.output
+
+    def test_scan_command_version(self, runner):
+        """Test version command output."""
+        result = runner.invoke(app, ["version"])
+        assert result.exit_code == 0
+        assert "AI Code Audit CLI" in result.output
+
+    def test_scan_command_languages(self, runner):
+        """Test languages command output."""
+        result = runner.invoke(app, ["languages"])
+        assert result.exit_code == 0
+        assert "Python" in result.output
+        assert "JavaScript" in result.output
+        assert "TypeScript" in result.output
+
+    def test_scan_nonexistent_file(self, runner):
+        """Test scanning nonexistent file."""
+        result = runner.invoke(app, ["scan", "/nonexistent/file.py"])
+        assert result.exit_code == 1
+        assert "Error" in result.output
+
+    def test_scan_directory(self, runner, test_files):
+        """Test scanning a directory."""
+        result = runner.invoke(app, ["scan", str(test_files)])
+        assert result.exit_code == 0
+        assert "AI Code Audit Results" in result.output or "Issues Found" in result.output
+
+    def test_scan_with_verbose(self, runner, test_files):
+        """Test scanning with verbose option."""
+        result = runner.invoke(app, ["scan", str(test_files), "--verbose"])
+        assert result.exit_code == 0
+
+    def test_scan_with_output_format(self, runner, test_files):
+        """Test scanning with output format option."""
+        result = runner.invoke(app, ["scan", str(test_files), "--format", "json"])
+        assert result.exit_code == 0
+
+    def test_scan_with_quiet_mode(self, runner, test_files):
+        """Test scanning with quiet mode."""
+        result = runner.invoke(app, ["scan", str(test_files), "--quiet"])
+        assert result.exit_code == 0
+        assert "Confidence Score" in result.output
+
+    def test_scan_with_language_filter(self, runner, test_files):
+        """Test scanning with language filter."""
+        result = runner.invoke(app, ["scan", str(test_files), "--language", "python"])
+        assert result.exit_code == 0
+
+    def test_scan_with_severity_filter(self, runner, test_files):
+        """Test scanning with severity filter."""
+        result = runner.invoke(app, ["scan", str(test_files), "--severity", "high"])
+        assert result.exit_code == 0
+
+    def test_scan_with_no_color(self, runner, test_files):
+        """Test scanning with no color option."""
+        result = runner.invoke(app, ["scan", str(test_files), "--no-color"])
+        assert result.exit_code == 0
+
+
+class TestOutputFormatter:
+    """Tests for output formatting."""
+
+    def test_get_score_color_green(self):
+        """Test score color for high scores."""
+        from src.cli.output import OutputFormatter
+        from src.cli.options import ScanOptions
+
+        options = ScanOptions()
+        formatter = OutputFormatter(options)
+        assert formatter._get_score_color(95) == "green"
+
+    def test_get_score_color_yellow(self):
+        """Test score color for medium scores."""
+        from src.cli.output import OutputFormatter
+        from src.cli.options import ScanOptions
+
+        options = ScanOptions()
+        formatter = OutputFormatter(options)
+        assert formatter._get_score_color(75) == "yellow"
+
+    def test_get_score_color_orange(self):
+        """Test score color for low-medium scores."""
+        from src.cli.output import OutputFormatter
+        from src.cli.options import ScanOptions
+
+        options = ScanOptions()
+        formatter = OutputFormatter(options)
+        assert formatter._get_score_color(55) == "orange1"
+
+    def test_get_score_color_red(self):
+        """Test score color for low scores."""
+        from src.cli.output import OutputFormatter
+        from src.cli.options import ScanOptions
+
+        options = ScanOptions()
+        formatter = OutputFormatter(options)
+        assert formatter._get_score_color(25) == "red"
+
+    def test_get_severity_style(self):
+        """Test severity style mapping."""
+        from src.cli.output import OutputFormatter
+        from src.cli.options import ScanOptions
+
+        options = ScanOptions()
+        formatter = OutputFormatter(options)
+
+        assert formatter._get_severity_style(SeverityLevel.CRITICAL) == "red bold"
+        assert formatter._get_severity_style(SeverityLevel.HIGH) == "orange1"
+        assert formatter._get_severity_style(SeverityLevel.MEDIUM) == "yellow"
+        assert formatter._get_severity_style(SeverityLevel.LOW) == "blue"