On Windows, if the Python "Scripts" directory is not in the PATH, and codecov is invoked like C:\...\Scripts\codecov, try_to_run will fail to exec coverage. The same could happen on Unix, but it is less likely.

This can be avoided a few ways, e.g. by calling coverage as a Python package, adding the "Scripts" directory to the PATH for the exec, using sys.executable -m coverage on Python 2.7+, etc.