diff --git a/src/attr/_make.py b/src/attr/_make.py
index 06bf6c19..c5d63e64 100644
--- a/src/attr/_make.py
+++ b/src/attr/_make.py
@@ -1244,12 +1244,13 @@ def make_class(name, attrs, bases=(object,), **attributes_arguments):
         {} if post_init is None else {"__attrs_post_init__": post_init}
     )
     # For pickling to work, the __module__ variable needs to be set to the
-    # frame where the class is created. Bypass this step in environments where
+    # frame where the class is created.  Bypass this step in environments where
     # sys._getframe is not defined (Jython for example) or sys._getframe is not
-    # defined for arguments greater than 0 (IronPython)
+    # defined for arguments greater than 0 (IronPython).
     try:
-        type_.__module__ = sys._getframe(1).f_globals.get('__name__',
-                                                          '__main__')
+        type_.__module__ = sys._getframe(1).f_globals.get(
+            "__name__", "__main__",
+        )
     except (AttributeError, ValueError):
         pass
 
diff --git a/tests/test_dark_magic.py b/tests/test_dark_magic.py
index 30d3425f..a8e66773 100644
--- a/tests/test_dark_magic.py
+++ b/tests/test_dark_magic.py
@@ -103,7 +103,7 @@ class WithMetaSlots(object):
     pass
 
 
-FromMakeClass = attr.make_class('FromMakeClass', ['x'])
+FromMakeClass = attr.make_class("FromMakeClass", ["x"])
 
 
 class TestDarkMagic(object):
diff --git a/tests/test_make.py b/tests/test_make.py
index a79372b5..55a65717 100644
--- a/tests/test_make.py
+++ b/tests/test_make.py
@@ -457,6 +457,7 @@ class TestMakeClass(object):
         attributes_arguments are passed to attributes
         """
         C = make_class("C", ["x"], repr=False)
+
         assert repr(C(1)).startswith("<tests.test_make.C object at 0x")
 
     def test_catches_wrong_attrs_type(self):
@@ -478,9 +479,11 @@ class TestMakeClass(object):
             pass
 
         cls = make_class("C", {})
+
         assert cls.__mro__[-1] == object
 
         cls = make_class("C", {}, bases=(D,))
+
         assert D in cls.__mro__
         assert isinstance(cls(), D)
 
@@ -501,7 +504,8 @@ class TestMakeClass(object):
         """
         monkeypatch.delattr(sys, '_getframe')
         C = make_class("C", ["x"])
-        assert C.__attrs_attrs__
+
+        assert 1 == len(C.__attrs_attrs__)
 
 
 class TestFields(object):
@@ -514,6 +518,7 @@ class TestFields(object):
         """
         with pytest.raises(TypeError) as e:
             fields(C(1, 2))
+
         assert "Passed object must be a class." == e.value.args[0]
 
     def test_handler_non_attrs_class(self, C):