Add raises docstrings.

gcloud/credentials.py

@@ -95,6 +95,8 @@ def _get_signed_query_params(credentials, expiration, string_to_sign):
     :type string_to_sign: string
     :param string_to_sign: The string to be signed by the credentials.
 
+    :raises AttributeError: If :meth: sign_blob is unavailable.
+
     :rtype: dict
     :returns: Query parameters matching the signing credentials with a
               signed payload.
@@ -123,6 +125,8 @@ def _get_expiration_seconds(expiration):
     :type expiration: int, long, datetime.datetime, datetime.timedelta
     :param expiration: When the signed URL should expire.
 
+    :raises TypeError: When expiration is not an integer.
+
     :rtype: int
     :returns: a timestamp as an absolute number of seconds.
     """

gcloud/test_credentials.py

@@ -114,8 +114,8 @@ def _callFUT(self, credentials, expiration, string_to_sign):
 
     def test_it(self):
         import base64
-        from gcloud._testing import _Monkey
-        from gcloud import credentials as MUT
+        # from gcloud._testing import _Monkey
+        # from gcloud import credentials as MUT
 
         SIG_BYTES = b'DEADBEEF'
         ACCOUNT_NAME = object()