include test files

Author: mscroggs

setup.py

@@ -46,7 +46,7 @@
 You can find information about how to contribute to Symfem [here](CONTRIBUTING.md).
 """
 
-data_files = ["LICENSE"]
+data_files = ["LICENSE", ("test", ["test/__init__.py", "test/utils.py", "test/conftest.py"])]
 
 if __name__ == "__main__":
     setuptools.setup(