"make coverage" does not run in python 3.7

[meadsteve]

On (at least) 3.7.2 it produces the following error:

============================================================ FAILURES =============================================================
___________________________________________ test_an_async_bound_function_can_be_mocked ____________________________________________

    @mock.patch("tests.bug_fixes.resources_for_189.an_async_bound_function", _fake_async)
    @pytest.mark.asyncio
    async def test_an_async_bound_function_can_be_mocked():
        from tests.bug_fixes.resources_for_189 import an_async_bound_function
        from tests.test_context_based_executions import SomeDep
    
>       assert await an_async_bound_function(SomeDep()) == "mocked"
E       AssertionError: assert 'ok' == 'mocked'
E         - mocked
E         + ok

tests/bug_fixes/test_189_lagom_functions_should_be_mockable.py:25: AssertionError