test: hide check_coverage source in pytest tracebacks
test: hide check_coverage source in pytest tracebacks

The code for the helper is uninteresting and long, and only makes it harder to
see what is going wrong.  Hide it.

https://docs.pytest.org/en/latest/example/simple.html#writing-well-integrated-assertion-helpers

hugovk/coveragepy,nedbat/coveragepy,nedbat/coveragepy,nedbat/coveragepy,hugovk/coveragepy,nedbat/coveragepy,hugovk/coveragepy,hugovk/coveragepy,nedbat/coveragepy,hugovk/coveragepy