diff --git a/tests/test_cli.py b/tests/test_cli.py
new file mode 100644
index 0000000..7a4f745
--- /dev/null
+++ b/tests/test_cli.py
@@ -0,0 +1,123 @@
+"""Tests for CLI interface."""
+
+import pytest
+from click.testing import CliRunner
+from pathlib import Path
+import tempfile
+import os
+
+from src.cli import cli, analyze, fix, rules, languages
+
+
+class TestCLI:
+    """Tests for CLI commands."""
+
+    def test_cli_group_exists(self):
+        assert cli is not None
+
+    def test_rules_command(self):
+        runner = CliRunner()
+        result = runner.invoke(rules)
+        assert result.exit_code == 0
+        assert "security" in result.output.lower() or "Rule ID" in result.output
+
+    def test_languages_command(self):
+        runner = CliRunner()
+        result = runner.invoke(languages)
+        assert result.exit_code == 0
+        assert "python" in result.output.lower()
+        assert "javascript" in result.output.lower()
+        assert "typescript" in result.output.lower()
+
+    def test_analyze_nonexistent_file(self):
+        runner = CliRunner()
+        result = runner.invoke(analyze, ["/nonexistent/path"])
+        assert result.exit_code != 0
+
+    def test_analyze_file_with_issues(self):
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".py", delete=False) as f:
+            f.write('result = eval("os.system(\'rm -rf /\')")\n')
+            f.write('password = "secret123"\n')
+            temp_path = f.name
+
+        try:
+            runner = CliRunner()
+            result = runner.invoke(analyze, [temp_path, "--json"])
+            assert result.exit_code == 0
+            assert "password" in result.output or "eval" in result.output
+        finally:
+            os.unlink(temp_path)
+
+    def test_analyze_file_without_issues(self):
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".py", delete=False) as f:
+            f.write("def hello():\n    print('Hello, World!')\n")
+            temp_path = f.name
+
+        try:
+            runner = CliRunner()
+            result = runner.invoke(analyze, [temp_path])
+            assert result.exit_code == 0
+        finally:
+            os.unlink(temp_path)
+
+    def test_analyze_with_fix_flag(self):
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".py", delete=False) as f:
+            f.write("result = eval('os.system(\"ls\")')\n")
+            temp_path = f.name
+
+        try:
+            runner = CliRunner()
+            result = runner.invoke(analyze, [temp_path, "--fix"])
+            assert result.exit_code == 0
+            assert "# eval(" in result.output or "Fixed" in result.output
+        finally:
+            backup_path = temp_path + ".bak"
+            if os.path.exists(backup_path):
+                os.unlink(backup_path)
+
+    def test_analyze_directory(self):
+        with tempfile.TemporaryDirectory() as tmpdir:
+            subdir = Path(tmpdir) / "subdir"
+            subdir.mkdir()
+
+            test_file = subdir / "test.py"
+            test_file.write_text("result = eval('test')\n")
+
+            runner = CliRunner()
+            result = runner.invoke(analyze, [tmpdir])
+            assert result.exit_code == 0
+
+    def test_analyze_unsupported_file_type(self):
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".txt", delete=False) as f:
+            f.write("This is a text file\n")
+            temp_path = f.name
+
+        try:
+            runner = CliRunner()
+            result = runner.invoke(analyze, [temp_path])
+            assert result.exit_code == 0
+        finally:
+            os.unlink(temp_path)
+
+
+class TestOutputFormatting:
+    """Tests for output formatting."""
+
+    def test_json_output(self):
+        with tempfile.NamedTemporaryFile(mode="w", suffix=".py", delete=False) as f:
+            f.write('password = "secret123"\n')
+            temp_path = f.name
+
+        try:
+            runner = CliRunner()
+            result = runner.invoke(analyze, [temp_path, "--json"])
+            assert result.exit_code == 0
+            import json
+            json_start = result.output.find('{')
+            json_end = result.output.rfind('}') + 1
+            json_output = result.output[json_start:json_end]
+            data = json.loads(json_output)
+            assert "files_analyzed" in data
+            assert "results" in data
+        finally:
+            os.unlink(temp_path)