Add coverage output to tests
Test that renderer prints single file tests okay
Fix bug that was preventing fail fast from working

This also adds exhaustive tests for the classes in runner.py
Make helpers correctly state the files they check

all_files helpers were stating that they were checking individual files when they were in fact checking the entire source directory. single file helpers were stating that they were checking the entire directory when they were only checking a single file. This fixes that probelm and adds ehxaustive helper tests.