Spelling fix.
Just use the mock functions directly, rather than having our own aliases.
Simplifying mocks to just return a constant string.
Don't mock out the environment, it's unnecessary.

All we're doing here is replacing os.environ with a dict with the same
contents. We shouldn't be mutating the environment in the first place,
and we aren't.
We have two copies of _patch_open, remove one.
Documenting how our mocks work.
__create__ isn't used in pkglib.
Merge pull request #41 from ahlmss/tests_refactoring

Tests refactoring