Add test case for timing out acquiring a lock

Added test for context manager lock acquisition timeout. Also fixed
the code to no longer call release when failing to acquire the lock.

src/lynk/lock.py

@@ -67,11 +67,11 @@ def __call__(self, lease_duration=20, timeout_seconds=300):
 
     @contextmanager
     def _context_manager(self, lease_duration, max_wait_seconds):
+        self.acquire(
+            lease_duration=lease_duration,
+            max_wait_seconds=max_wait_seconds,
+        )
         try:
-            self.acquire(
-                lease_duration=lease_duration,
-                max_wait_seconds=max_wait_seconds,
-            )
             yield
         finally:
             self.release()

tests/unit/test_lock.py

@@ -6,6 +6,7 @@
 from lynk.techniques import BaseTechnique
 from lynk.refresh import LockRefresherFactory
 from lynk.refresh import LockRefresher
+from lynk.exceptions import LockNotGrantedError
 
 
 @pytest.fixture
@@ -53,6 +54,20 @@ def test_context_manager_does_acquire_and_release(self, create_lock):
         tech.acquire.assert_called_with('lock name', 20, max_wait_seconds=300)
         tech.release.assert_called_with('lock name')
 
+    def test_lock_not_granted_does_escape_context_manager(self, create_lock):
+        # The context manager swallows errors, its important that the
+        # LockNotGrantedError escapes this otherwise it could be silenced and
+        # the with block would exceute and operate on a resource protected by
+        # the lock, even though the lock acquisition failed.
+        # Also the release should not be called, since the acquire failed.
+        lock, tech, _ = create_lock()
+        tech.acquire.side_effect = LockNotGrantedError()
+        with pytest.raises(LockNotGrantedError):
+            with lock():
+                pass
+        tech.acquire.assert_called_with('lock name', 20, max_wait_seconds=300)
+        tech.release.assert_not_called()
+
     def test_acquire_does_create_and_start_refresher(self, create_lock):
         lock, tech, refresher_factory = create_lock(refresher=True)
         mock_refresher = mock.Mock(spec=LockRefresher)