test(linux_client): add test_client_certificate_validity_and_proactive_check in test_linux_client.py

tests/test_linux_client.py

@@ -223,6 +223,27 @@ class TestLinuxClientComponent(unittest.TestCase):
         finally:
             shutil.rmtree(test_dir, ignore_errors=True)
 
+    def test_client_certificate_validity_and_proactive_check(self):
+        import shutil
+        test_dir = "test_linux_client_validity"
+        os.makedirs(test_dir, exist_ok=True)
+        try:
+            from src import server_enrollment as se
+            ca_cert, ca_key, _, _ = se.generate_ca_if_needed(test_dir)
+            client_cert_pem, client_key_pem = se.issue_client_cert("linux-validity-test", ca_cert, ca_key, days_valid=365)
+            cert_path = os.path.join(test_dir, "client.crt")
+            with open(cert_path, "w", encoding="utf-8") as f:
+                f.write(client_cert_pem)
+
+            # Newly issued cert (365 days) is not expiring soon at 30 days
+            self.assertFalse(Linux_Client.is_cert_expiring_soon(cert_path, threshold_days=30))
+            # Large threshold (500 days) reports expiring soon
+            self.assertTrue(Linux_Client.is_cert_expiring_soon(cert_path, threshold_days=500))
+            # Non-existent file reports expiring / missing
+            self.assertTrue(Linux_Client.is_cert_expiring_soon(os.path.join(test_dir, "missing.crt")))
+        finally:
+            shutil.rmtree(test_dir, ignore_errors=True)
+
 
 if __name__ == "__main__":
     unittest.main()