fixed a potential inconsistency between a successful PGPKey.unlock and one that warns that the operation did nothing if it is invoked with an "as ..." clause; updated relevant tests to check that

pgpy/pgp.py

@@ -1313,13 +1313,13 @@ class PGPKey(PGPObject, Armorable):
         if self.is_public:
             # we can't unprotect public keys because only private key material is ever protected
             warnings.warn("Public keys cannot be passphrase-protected", stacklevel=3)
-            yield
+            yield self
             return
 
         if not self.is_protected:
             # we can't unprotect private keys that are not protected, because there is no ciphertext to decrypt
             warnings.warn("This key is not protected with a passphrase", stacklevel=3)
-            yield
+            yield self
             return
 
         try:

tests/test_05_actions.py

@@ -230,7 +230,8 @@ class TestPGPKey(object):
         assert sec.is_protected is False
 
         # unlock with the correct passphrase
-        with enc.unlock('QwertyUiop'), self.assert_warnings():
+        with enc.unlock('QwertyUiop') as _unlocked, self.assert_warnings():
+            assert _unlocked is enc
             assert enc.is_unlocked
 
     def test_verify_detached(self, sigkey, sigsig, sigsubj):

tests/test_10_exceptions.py

@@ -49,16 +49,16 @@ def targette_sec():
 
 class TestPGPKey(object):
     def test_unlock_pubkey(self, rsa_pub, recwarn):
-        with rsa_pub.unlock("QwertyUiop"):
-            pass
+        with rsa_pub.unlock("QwertyUiop") as _unlocked:
+            assert _unlocked is rsa_pub
 
         w = recwarn.pop(UserWarning)
         assert str(w.message) == "Public keys cannot be passphrase-protected"
         assert w.filename == __file__
 
     def test_unlock_not_protected(self, rsa_sec, recwarn):
-        with rsa_sec.unlock("QwertyUiop"):
-            pass
+        with rsa_sec.unlock("QwertyUiop") as _unlocked:
+            assert _unlocked is rsa_sec
 
         w = recwarn.pop(UserWarning)
         assert str(w.message) == "This key is not protected with a passphrase"