diff --git a/test/unit/test_providers_base_master_key.py b/test/unit/test_providers_base_master_key.py
index 86a256c97..26a90ced8 100644
--- a/test/unit/test_providers_base_master_key.py
+++ b/test/unit/test_providers_base_master_key.py
@@ -11,11 +11,8 @@
 # ANY KIND, either express or implied. See the License for the specific
 # language governing permissions and limitations under the License.
 """Test suite for aws_encryption_sdk.key_providers.base.MasterKey"""
-import unittest
-
 import attr
 import pytest
-import six
 from mock import MagicMock, patch, sentinel
 
 from aws_encryption_sdk.exceptions import ConfigMismatchError, IncorrectMasterKeyError, InvalidKeyIdError
@@ -63,12 +60,13 @@ class FakeMasterKey(MockMasterKey):
     excinfo.match(r'MasterKey config classes must have a "provider_id" attribute defined.')
 
 
-class TestMasterKey(unittest.TestCase):
-    def setUp(self):
+class TestMasterKey(object):
+    @pytest.fixture(autouse=True)
+    def apply_fixture(self):
         self.mock_data_key_len_check_patcher = patch("aws_encryption_sdk.internal.utils.source_data_key_length_check")
         self.mock_data_key_len_check = self.mock_data_key_len_check_patcher.start()
-
-    def tearDown(self):
+        yield
+        # Run tearDown
         self.mock_data_key_len_check_patcher.stop()
 
     def test_parent(self):
@@ -85,8 +83,9 @@ def _encrypt_data_key(self, data_key, algorithm, encryption_context):
             def _decrypt_data_key(self, encrypted_data_key, algorithm, encryption_context):
                 pass
 
-        with six.assertRaisesRegex(self, TypeError, "Can't instantiate abstract class TestMasterKey *"):
+        with pytest.raises(TypeError) as excinfo:
             TestMasterKey()
+        excinfo.match("Can't instantiate abstract class TestMasterKey *")
 
     def test_generate_data_key_enforcement(self):
         class TestMasterKey(MasterKey):
@@ -98,8 +97,9 @@ def _encrypt_data_key(self, data_key, algorithm, encryption_context):
             def _decrypt_data_key(self, encrypted_data_key, algorithm, encryption_context):
                 pass
 
-        with six.assertRaisesRegex(self, TypeError, "Can't instantiate abstract class TestMasterKey *"):
+        with pytest.raises(TypeError) as excinfo:
             TestMasterKey()
+        excinfo.match("Can't instantiate abstract class TestMasterKey *")
 
     def test_encrypt_data_key_enforcement(self):
         class TestMasterKey(MasterKey):
@@ -111,8 +111,9 @@ def _generate_data_key(self, algorithm, encryption_context):
             def _decrypt_data_key(self, encrypted_data_key, algorithm, encryption_context):
                 pass
 
-        with six.assertRaisesRegex(self, TypeError, "Can't instantiate abstract class TestMasterKey *"):
+        with pytest.raises(TypeError) as excinfo:
             TestMasterKey()
+        excinfo.match("Can't instantiate abstract class TestMasterKey *")
 
     def test_decrypt_data_key_enforcement(self):
         class TestMasterKey(MasterKey):
@@ -124,8 +125,9 @@ def _generate_data_key(self, algorithm, encryption_context):
             def _encrypt_data_key(self, data_key, algorithm, encryption_context):
                 pass
 
-        with six.assertRaisesRegex(self, TypeError, "Can't instantiate abstract class TestMasterKey *"):
+        with pytest.raises(TypeError) as excinfo:
             TestMasterKey()
+        excinfo.match("Can't instantiate abstract class TestMasterKey *")
 
     def test_new(self):
         mock_master_key = MockMasterKey(
@@ -142,10 +144,9 @@ def test_new_conf_mismatch(self):
         mock_config = MagicMock()
         mock_config.__class__ = MockMasterKeyConfig
         mock_config.provider_id = sentinel.mismatched_provider_id
-        with six.assertRaisesRegex(
-            self, ConfigMismatchError, "Config provider_id does not match MasterKey provider_id: *"
-        ):
+        with pytest.raises(ConfigMismatchError) as excinfo:
             MockMasterKey(config=mock_config)
+        excinfo.match("Config provider_id does not match MasterKey provider_id: *")
 
     def test_owns_data_key_owned(self):
         mock_master_key = MockMasterKey(
@@ -220,8 +221,9 @@ def test_new_master_key_invalid(self):
             mock_encrypted_data_key=sentinel.encrypted_data_key,
             mock_decrypted_data_key=sentinel.decrypted_data_key,
         )
-        with six.assertRaisesRegex(self, InvalidKeyIdError, "MasterKeys can only provide themselves. *"):
+        with pytest.raises(InvalidKeyIdError) as excinfo:
             mock_master_key._new_master_key(sentinel.another_key_id)
+        excinfo.match("MasterKeys can only provide themselves. *")
 
     def test_key_check_valid(self):
         mock_master_key = MockMasterKey(
@@ -243,8 +245,9 @@ def test_key_check_invalid(self):
         )
         mock_data_key = MagicMock()
         mock_data_key.key_provider = sentinel.another_key_provider
-        with six.assertRaisesRegex(self, IncorrectMasterKeyError, "Provided data key provider *"):
+        with pytest.raises(IncorrectMasterKeyError) as excinfo:
             mock_master_key._key_check(mock_data_key)
+        excinfo.match("Provided data key provider *")
 
     def test_generate_data_key(self):
         mock_master_key = MockMasterKey(