add invaliditydate class for crl entry extensions
diff --git a/tests/test_x509.py b/tests/test_x509.py
index 757df44..560324b 100644
--- a/tests/test_x509.py
+++ b/tests/test_x509.py
@@ -387,9 +387,9 @@
             x509.CertificateIssuer).value
         assert issuer == x509.CertificateIssuer(exp_issuer)
 
-        date = rev1.extensions.get_extension_for_oid(
-            x509.OID_INVALIDITY_DATE).value
-        assert date == datetime.datetime(2015, 1, 1, 0, 0)
+        date = rev1.extensions.get_extension_for_class(
+            x509.InvalidityDate).value
+        assert date == x509.InvalidityDate(datetime.datetime(2015, 1, 1, 0, 0))
 
         # Check if all reason flags can be found in the CRL.
         flags = set(x509.ReasonFlags)
diff --git a/tests/test_x509_ext.py b/tests/test_x509_ext.py
index b8105a4..91a0765 100644
--- a/tests/test_x509_ext.py
+++ b/tests/test_x509_ext.py
@@ -5,6 +5,7 @@
 from __future__ import absolute_import, division, print_function
 
 import binascii
+import datetime
 import ipaddress
 import os
 
@@ -135,6 +136,29 @@
         )
 
 
+class TestInvalidityDate(object):
+    def test_invalid_invalidity_date(self):
+        with pytest.raises(TypeError):
+            x509.InvalidityDate("notadate")
+
+    def test_eq(self):
+        invalid1 = x509.InvalidityDate(datetime.datetime(2015, 1, 1, 1, 1))
+        invalid2 = x509.InvalidityDate(datetime.datetime(2015, 1, 1, 1, 1))
+        assert invalid1 == invalid2
+
+    def test_ne(self):
+        invalid1 = x509.InvalidityDate(datetime.datetime(2015, 1, 1, 1, 1))
+        invalid2 = x509.InvalidityDate(datetime.datetime(2015, 1, 1, 1, 2))
+        assert invalid1 != invalid2
+        assert invalid1 != object()
+
+    def test_repr(self):
+        invalid1 = x509.InvalidityDate(datetime.datetime(2015, 1, 1, 1, 1))
+        assert repr(invalid1) == (
+            "<InvalidityDate(invalidity_date=2015-01-01 01:01:00)>"
+        )
+
+
 class TestNoticeReference(object):
     def test_notice_numbers_not_all_int(self):
         with pytest.raises(TypeError):