[Tests] Run fast test suite in clean environment

[reasonablytall]

Fixes #2181

This makes npm run test/fast start the test suite from within a fresh login shell, effectively removing the NPM_CONFIG_... variables that caused most tests to fail in #2181. I've run this in both zsh and bash, and all fast tests pass.

$TERM is included in the fresh environment to prevent tests that rely on the color output of nvm_print_formatted_alias from failing.

node_modules/.bin is still added to the path by the makefile, so I temporarily remove it in test/fast/Running "nvm use iojs" uses latest io.js version for the same reason as #2322.

This change could probably work for the other suites too! I just haven't dug into that yet... let me know what you think! :)

[reasonablytall]

@memark if you have the time could you run npm run test/fast from this branch? Want to make sure it's not just working on my machine 😄

[memark]

@reasonablytall This is the only test failing now in your branch:

    ✗ nvm_die_on_prefix
'nvm_die_on_prefix 0 foo' did not error with 'nvm is not compatible with the npm config "prefix" option: currently set to "./bad prefix"
Run `npm config delete prefix` or `foo` to unset it.' with bad prefix set; got 'nvm is not compatible with the npm config "prefix" option: currently set to "./bad prefix"
Run `npm config delete prefix` or `foo` to unset it.
Make sure your username (memark) matches the one in your $HOME path.
See the "macOS Troubleshooting" section in the docs for more information.'

On a sidenote, I had to enter my password (sudo somewhere?), which I did. I don't remember if I had to do that last time (it's been a while).

[reasonablytall]

Thanks for the check @memark! The sudo request is a normal part of the test suite :)

It looks like that failing test is doing everything correctly, but an added help message exclusive to MacOS causes the output to be different from expected (which I think explains why the test passes on my linux machine, as well as on CI). Previously nvm_die_on_prefix failed at an earlier step (as seen in #2181), so we never saw this particular failure.

I figure that this PR can be reviewed as-is, and I can fix nvm_die_on_prefix in a separate PR. @ljharb does that sound reasonable to you?

[ljharb]

can you help me understand these changes? env i get, you're setting up the $TERM variable. What does -lc do? I see /bin/bash, what happens if that's not the path to bash, and what about all the other shells (zsh, sh, dash, ksh)?

[reasonablytall]

I'll break down my thinking:

• env -i runs the following in a fully cleared environment
• TERM="$TERM" brings $TERM into that environment
• /bin/bash -lc runs the make command in a login (-l) shell which first populates the environment by executing various profile files. I figure that running from a login shell is more ~robust~ than running from a blank environment, though I'm definitely not sure. When I run the same command without -l the tests all pass but the git checks at the start fail due to a path issue.

Using /bin/bash was an oversight. Both bash and sh work, and I'll make a change to use bash instead (since sh doesn't list -l as an option in the man page) unless you prefer otherwise.

The shell urchin uses to run the tests is taken from the make target test-$shell, so the shell used to run make doesn't matter.

[ljharb]

LGTM! Ci for this repo is currently broken; once it's fixed, i'll rebase and land this.