diff --git a/tests/test_scanner.py b/tests/test_scanner.py
new file mode 100644
index 0000000..3b5625b
--- /dev/null
+++ b/tests/test_scanner.py
@@ -0,0 +1,65 @@
+"""Tests for code scanner."""
+
+import pytest
+from pathlib import Path
+
+from src.core.scanner import CodeScanner
+from src.core.models import IssueCategory, SeverityLevel
+
+
+class TestCodeScanner:
+    """Tests for CodeScanner class."""
+
+    def test_scanner_initialization(self):
+        """Test scanner creates empty issue list."""
+        scanner = CodeScanner()
+        assert scanner.issues == []
+
+    def test_supported_extensions(self):
+        """Test supported file extensions."""
+        scanner = CodeScanner()
+        assert ".py" in scanner.SUPPORTED_EXTENSIONS
+        assert ".js" in scanner.SUPPORTED_EXTENSIONS
+        assert ".ts" in scanner.SUPPORTED_EXTENSIONS
+
+    def test_scan_single_file(self, tmp_path):
+        """Test scanning a single file."""
+        test_file = tmp_path / "test.py"
+        test_file.write_text("""
+def hello():
+    # TODO: implement
+    print("Hello")
+""")
+
+        scanner = CodeScanner()
+        result = scanner.scan(test_file)
+
+        assert result.files_scanned == 1
+        assert len(result.issues) == 1
+        assert result.issues[0].category == IssueCategory.MAINTAINABILITY
+        assert result.issues[0].severity == SeverityLevel.LOW
+
+    def test_scan_directory(self, tmp_path):
+        """Test scanning a directory."""
+        test_dir = tmp_path / "project"
+        test_dir.mkdir()
+
+        (test_dir / "test.py").write_text("# TODO: test")
+        (test_dir / "test.js").write_text("// FIXME: fix")
+
+        scanner = CodeScanner()
+        result = scanner.scan(test_dir)
+
+        assert result.files_scanned == 2
+        assert len(result.issues) == 2
+
+    def test_unsupported_file(self, tmp_path):
+        """Test skipping unsupported files."""
+        test_file = tmp_path / "test.txt"
+        test_file.write_text("TODO: something")
+
+        scanner = CodeScanner()
+        result = scanner.scan(test_file)
+
+        assert result.files_scanned == 0
+        assert len(result.issues) == 0