Add mypy config for tests directory (#991)

Author: florimondmanca

setup.cfg

@@ -6,6 +6,10 @@ max-line-length = 88
 disallow_untyped_defs = True
 ignore_missing_imports = True
 
+[mypy-tests.*]
+disallow_untyped_defs = False
+check_untyped_defs = True
+
 [tool:isort]
 combine_as_imports = True
 force_grid_wrap = 0