diff --git a/tests/unit/test_checks.py b/tests/unit/test_checks.py
new file mode 100644
index 0000000..fcff78c
--- /dev/null
+++ b/tests/unit/test_checks.py
@@ -0,0 +1,121 @@
+import pytest
+from unittest.mock import Mock, patch
+from depaudit.utils.version import (
+    parse_version,
+    compare_versions,
+    is_version_outdated,
+    extract_version_from_specifier,
+)
+
+
+class TestVersionParsing:
+    def test_parse_version_valid(self):
+        v = parse_version("1.2.3")
+        assert v is not None
+        assert str(v) == "1.2.3"
+
+    def test_parse_version_with_prerelease(self):
+        v = parse_version("1.2.3-beta.1")
+        assert v is not None
+
+    def test_parse_version_invalid(self):
+        v = parse_version("not-a-version")
+        assert v is None
+
+
+class TestVersionComparison:
+    def test_compare_versions_equal(self):
+        assert compare_versions("1.2.3", "1.2.3") == 0
+
+    def test_compare_versions_greater(self):
+        assert compare_versions("2.0.0", "1.2.3") == 1
+
+    def test_compare_versions_less(self):
+        assert compare_versions("1.2.3", "2.0.0") == -1
+
+
+class TestIsVersionOutdated:
+    def test_outdated_version(self):
+        assert is_version_outdated("1.0.0", "1.1.0") is True
+
+    def test_current_version(self):
+        assert is_version_outdated("1.1.0", "1.1.0") is False
+
+
+class TestLicenseChecking:
+    def test_normalize_mit_license(self):
+        from depaudit.checks.licenses import normalize_license
+        assert normalize_license("MIT") == "mit"
+
+    def test_normalize_apache_license(self):
+        from depaudit.checks.licenses import normalize_license
+        assert normalize_license("Apache-2.0") == "apache-2.0"
+
+    def test_normalize_gpl_license(self):
+        from depaudit.checks.licenses import normalize_license
+        assert normalize_license("GPL-3.0") == "gpl-3.0"
+
+    def test_check_license_allowlist(self):
+        from depaudit.checks.licenses import check_license
+        license_info = check_license("test-package", "MIT")
+        assert license_info.license_type == "mit"
+        assert license_info.is_spdx_compliant is True
+
+
+class TestValidateLicenseCompliance:
+    def test_validate_allowed_license(self):
+        from depaudit.checks.licenses import check_license, validate_license_compliance
+        license_info = check_license("test-package", "MIT")
+        is_compliant, message = validate_license_compliance(
+            license_info, ["MIT"], ["GPL-3.0"]
+        )
+        assert is_compliant is True
+
+    def test_validate_blocked_license(self):
+        from depaudit.checks.licenses import check_license, validate_license_compliance
+        license_info = check_license("test-package", "GPL-3.0")
+        is_compliant, message = validate_license_compliance(
+            license_info, ["MIT"], ["GPL-3.0"]
+        )
+        assert is_compliant is False
+
+
+class TestOutdatedChecking:
+    @patch("depaudit.checks.outdated.NPMClient.get_latest_version")
+    def test_check_outdated_package(self, mock_get_latest):
+        mock_get_latest.return_value = "4.18.0"
+
+        from depaudit.checks.outdated import check_outdated
+        result = check_outdated("express", "4.17.1", "javascript")
+
+        assert result is not None
+        assert result.package_name == "express"
+        assert result.latest_version == "4.18.0"
+        assert result.minor_available is True
+
+
+class TestVulnerabilityChecker:
+    def test_vulnerability_to_dict(self):
+        from depaudit.checks.vulnerabilities import Vulnerability
+
+        vuln = Vulnerability(
+            id="CVE-2023-0001",
+            package_name="test-package",
+            current_version="1.0.0",
+            severity="high",
+            title="Test Vulnerability",
+            description="A test vulnerability",
+            affected_versions=["<1.1.0"],
+            fixed_version="1.1.0",
+            published="2023-01-01",
+            modified="2023-01-02",
+            cvss_score=7.5,
+            cwe=["CWE-79"],
+            references=["https://example.com"],
+            source="OSV",
+        )
+
+        result = vuln.to_dict()
+
+        assert result["id"] == "CVE-2023-0001"
+        assert result["severity"] == "high"