Add google.auth.jwt (#7)

diff --git a/tests/test__helpers.py b/tests/test__helpers.py
index b7e0bab..c2bc4a7 100644
--- a/tests/test__helpers.py
+++ b/tests/test__helpers.py
@@ -12,12 +12,24 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import datetime
 
 import pytest
 
 from google.auth import _helpers
 
 
+def test_utcnow():
+    assert isinstance(_helpers.utcnow(), datetime.datetime)
+
+
+def test_datetime_to_secs():
+    assert _helpers.datetime_to_secs(
+        datetime.datetime(1970, 1, 1)) == 0
+    assert _helpers.datetime_to_secs(
+        datetime.datetime(1990, 5, 29)) == 643939200
+
+
 def test_to_bytes_with_bytes():
     value = b'bytes-val'
     assert _helpers.to_bytes(value) == value