🛡️ Sentinel: [MEDIUM] Fix test suite SSRF mock bypass

[ManupaKDU]

🚨 Severity: MEDIUM
💡 Vulnerability: The test test_is_reachable_failure was using a private IP address (10.0.0.1). Because the application's SSRF filter blocks private IPs, it returned False immediately, bypassing the mocked subprocess.call. As a result, the test was silently passing without actually covering the intended subprocess failure branch.
🎯 Impact: The test suite was not correctly verifying the application's ability to handle network ping failures. Future refactors could break failure handling without triggering test regressions.
🔧 Fix: Changed the mocked test IP to a globally routable public IP (8.8.4.4) to properly reach the subprocess call logic. Added mock_call.assert_called_once() to ensure the mock is always evaluated properly.
✅ Verification: Ran python3 -m unittest test_testping1.py and confirmed all tests pass with the mock fully executing.

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PR created automatically by Jules for task 16557653444664257341 started by @ManupaKDU

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