test: fix broken test

Signed-off-by: Alexander Tkachev <sasha64sasha@gmail.com>

cloudevents/tests/test_generic_cloudevent.py

@@ -6,7 +6,7 @@ def test_del_is_abstract():
     """
     exists mainly for coverage reasons
     """
-    with pytest.raises(TypeError):
+    with pytest.raises(NotImplementedError):
         del CloudEvent()["a"]
 
 
@@ -14,7 +14,7 @@ def test_set_is_abstract():
     """
     exists mainly for coverage reasons
     """
-    with pytest.raises(TypeError):
+    with pytest.raises(NotImplementedError):
         CloudEvent()["a"] = 2
 
 
@@ -22,14 +22,15 @@ def test_create_is_abstract():
     """
     exists mainly for coverage reasons
     """
-    assert CloudEvent.create({}, None) is None
+    with pytest.raises(NotImplementedError):
+        assert CloudEvent.create({}, None) is None
 
 
 def test_data_read_is_abstract():
     """
     exists mainly for coverage reasons
     """
-    with pytest.raises(TypeError):
+    with pytest.raises(NotImplementedError):
         CloudEvent()._data_read_model
 
 
@@ -37,5 +38,5 @@ def test_attributes_read_model_is_abstract():
     """
     exists mainly for coverage reasons
     """
-    with pytest.raises(TypeError):
+    with pytest.raises(NotImplementedError):
         CloudEvent()._attributes_read_model