Test lock releases with/without arguments

StrictLock and CompositeLock can be used as context managers in 2 ways.
They are context manager classes (__enter__ and __exit__ methods) but
the __call__ method is a generator context manager too - allowing
arguments.

This code now tests both forms.

tests/test_sync_lock.py

@@ -112,9 +112,29 @@ def g():
 class DummyException(Exception):
     pass
 
-def test_rlock_released_after_error(this_lock):
+def test_rlock_released_after_error_args(this_lock):
+    """If an exception occurs in a with block, the lock should release.
+    
+    NB there are two sets of code that do this - one if arguments are 
+    given (i.e. the __call__ method of the lock class) and one without
+    arguments (i.e. the __enter__ and __exit__ methods).
+
+    See the following function for the no-arguments version.
+    """
+    try:
+        with this_lock():
+            assert this_lock.locked()
+            raise DummyException()
+    except DummyException:
+        pass
+    assert not this_lock.locked()
+
+def test_rlock_released_after_error_noargs(this_lock):
+    """If an exception occurs in a with block, the lock should release."""
     try:
         with this_lock:
+            assert this_lock.locked()
             raise DummyException()
     except DummyException:
-        assert not this_lock.locked()
+        pass
+    assert not this_lock.locked()