with_env now overrides the environment, similar to with_stdin
an additional function update_env was created to mirror the prior
functionality of with_env, updating the env
This was changed as previously it was impossible to delete variables
from the env
replaced the code of .ok() with a call to .expect, to remove the code
duplication
Change-Id: I83933893c7f2ccfdc7bd4933b7592b475c435e76
Commentator2.0
dbff52bfbc