Stats from git: Who writes tests and who does not?

Our python applications get store in a git repo which has roughly this structure:

fooapp/setup.py
fooapp/fooapp/
fooapp/fooapp/tests/
fooapp/fooapp/tests/test_foo.pa
fooapp/fooapp/file1.py
fooapp/fooapp/file2.py
fooapp/fooapp/submodule/file3.py
...

I would like to know: Who writes tests and who does not.

More precise: During the last N weeks for every developer, how many lines were added in the tests directory and how many in the production code (file1.py, file2.py, ...)

This gives me two numbers per developer.

What is the most simple way to solve this (with open source tools)?