diff --git a/tests/test_scanners.py b/tests/test_scanners.py
new file mode 100644
index 0000000..86ca7d9
--- /dev/null
+++ b/tests/test_scanners.py
@@ -0,0 +1,181 @@
+"""Tests for scanner modules."""
+
+import pytest
+from pathlib import Path
+
+from src.core.models import Issue, IssueCategory, SeverityLevel
+from src.scanners.bandit_scanner import BanditScanner
+from src.scanners.ruff_scanner import RuffScanner
+from src.scanners.tree_sitter_scanner import TreeSitterScanner
+
+
+class TestBanditScanner:
+    """Tests for BanditScanner."""
+
+    def test_scan_content_returns_list(self, sample_python_code):
+        """Test that scan_content returns a list of issues."""
+        scanner = BanditScanner()
+        issues = scanner.scan_content(sample_python_code, "/test/file.py")
+        assert isinstance(issues, list)
+
+    def test_scan_content_handles_empty_code(self):
+        """Test that scan_content handles empty code."""
+        scanner = BanditScanner()
+        issues = scanner.scan_content("", "/test/file.py")
+        assert isinstance(issues, list)
+
+    def test_scan_content_handles_invalid_code(self):
+        """Test that scan_content handles invalid code gracefully."""
+        scanner = BanditScanner()
+        issues = scanner.scan_content("not valid python", "/test/file.py")
+        assert isinstance(issues, list)
+
+    def test_scan_file_nonexistent(self):
+        """Test that scan_file handles nonexistent files."""
+        scanner = BanditScanner()
+        issues = scanner.scan_file("/nonexistent/file.py")
+        assert issues == []
+
+    def test_get_plugin_info(self):
+        """Test that get_plugin_info returns valid info."""
+        scanner = BanditScanner()
+        info = scanner.get_plugin_info()
+        assert "name" in info
+        assert "version" in info
+        assert info["name"] == "bandit"
+
+
+class TestRuffScanner:
+    """Tests for RuffScanner."""
+
+    def test_scan_content_returns_list(self, clean_python_code):
+        """Test that scan_content returns a list of issues."""
+        scanner = RuffScanner()
+        issues = scanner.scan_content(clean_python_code, "/test/file.py", "python")
+        assert isinstance(issues, list)
+
+    def test_scan_content_handles_empty_code(self):
+        """Test that scan_content handles empty code."""
+        scanner = RuffScanner()
+        issues = scanner.scan_content("", "/test/file.py", "python")
+        assert isinstance(issues, list)
+
+    def test_scan_content_handles_unparseable_code(self):
+        """Test that scan_content handles unparseable code."""
+        scanner = RuffScanner()
+        issues = scanner.scan_content("def (", "/test/file.py", "python")
+        assert isinstance(issues, list)
+
+    def test_detect_language_python(self):
+        """Test language detection for Python files."""
+        scanner = RuffScanner()
+        assert scanner._detect_language("/test/file.py") == "python"
+
+    def test_detect_language_javascript(self):
+        """Test language detection for JavaScript files."""
+        scanner = RuffScanner()
+        assert scanner._detect_language("/test/file.js") == "javascript"
+
+    def test_detect_language_typescript(self):
+        """Test language detection for TypeScript files."""
+        scanner = RuffScanner()
+        assert scanner._detect_language("/test/file.ts") == "typescript"
+
+    def test_get_plugin_info(self):
+        """Test that get_plugin_info returns valid info."""
+        scanner = RuffScanner()
+        info = scanner.get_plugin_info()
+        assert "name" in info
+        assert info["name"] == "ruff"
+
+
+class TestTreeSitterScanner:
+    """Tests for TreeSitterScanner."""
+
+    def test_scan_content_returns_list(self, sample_python_code):
+        """Test that scan_content returns a list of issues."""
+        scanner = TreeSitterScanner()
+        issues = scanner.scan_content(sample_python_code, "/test/file.py", "python")
+        assert isinstance(issues, list)
+
+    def test_scan_python_finds_credentials(self):
+        """Test that scanner finds hardcoded credentials in Python."""
+        code = 'api_key = "sk-1234567890abcdefghijklmnop"'
+        scanner = TreeSitterScanner()
+        issues = scanner.scan_content(code, "/test/file.py", "python")
+
+        credential_issues = [i for i in issues if i.category == IssueCategory.SECURITY]
+        assert len(credential_issues) > 0
+
+    def test_scan_python_finds_mutable_defaults(self):
+        """Test that scanner finds mutable default arguments."""
+        code = "def func(items=[]):\n    pass"
+        scanner = TreeSitterScanner()
+        issues = scanner.scan_content(code, "/test/file.py", "python")
+
+        anti_pattern_issues = [i for i in issues if i.category == IssueCategory.ANTI_PATTERN]
+        assert len(anti_pattern_issues) > 0
+
+    def test_scan_python_finds_bare_except(self):
+        """Test that scanner finds bare except clauses."""
+        code = "try:\n    pass\nexcept:\n    pass"
+        scanner = TreeSitterScanner()
+        issues = scanner.scan_content(code, "/test/file.py", "python")
+
+        error_handling_issues = [i for i in issues if i.category == IssueCategory.ERROR_HANDLING]
+        assert len(error_handling_issues) > 0
+
+    def test_scan_js_finds_credentials(self):
+        """Test that scanner finds credentials in JavaScript."""
+        code = 'const apiKey = "sk_live_1234567890abcdefghijklmnopqrstuvwxyz";'
+        scanner = TreeSitterScanner()
+        issues = scanner.scan_content(code, "/test/file.js", "javascript")
+
+        security_issues = [i for i in issues if i.category == IssueCategory.SECURITY]
+        assert len(security_issues) > 0
+
+    def test_scan_sql_injection_patterns(self):
+        """Test that scanner finds SQL injection patterns."""
+        code = 'result = db.execute(f"SELECT * FROM users WHERE name = {user_input}")'
+        scanner = TreeSitterScanner()
+        issues = scanner.scan_content(code, "/test/file.py", "python")
+
+        security_issues = [i for i in issues if i.category == IssueCategory.SECURITY]
+        assert len(security_issues) > 0
+
+    def test_scan_command_injection_patterns(self):
+        """Test that scanner finds command injection patterns."""
+        code = 'os.system(f"echo {user_input}")'
+        scanner = TreeSitterScanner()
+        issues = scanner.scan_content(code, "/test/file.py", "python")
+
+        security_issues = [i for i in issues if i.category == IssueCategory.SECURITY]
+        assert len(security_issues) > 0
+
+    def test_false_positive_filtering(self):
+        """Test that scanner filters false positives."""
+        code = '# TODO: Replace "sk-test-EXAMPLE" with real key'
+        scanner = TreeSitterScanner()
+        issues = scanner.scan_content(code, "/test/file.py", "python")
+
+        assert len(issues) == 0
+
+    def test_get_plugin_info(self):
+        """Test that get_plugin_info returns valid info."""
+        scanner = TreeSitterScanner()
+        info = scanner.get_plugin_info()
+        assert "name" in info
+        assert info["name"] == "tree-sitter"
+
+    def test_is_comment_detection(self):
+        """Test comment detection."""
+        scanner = TreeSitterScanner()
+        assert scanner._is_comment("# This is a comment") is True
+        assert scanner._is_comment("code = 1") is False
+
+    def test_language_detection(self):
+        """Test language detection from file path."""
+        scanner = TreeSitterScanner()
+        assert scanner._detect_language("/test/file.py") == "python"
+        assert scanner._detect_language("/test/file.js") == "javascript"
+        assert scanner._detect_language("/test/file.ts") == "typescript"