chore: import upstream snapshot with attribution

mpmath/tests/test_mpmath.py

@@ -0,0 +1,7 @@
+from mpmath import fp, iv, mp, mpc, mpf
+
+
+def test_newstyle_classes():
+    for cls in [mp, fp, iv, mpf, mpc]:
+        for s in cls.__class__.__mro__:
+            assert isinstance(s, type)