Fix a failing test introduced in #28.

[mr-salty]

The environment variables in the 'fails if env vars are set' test
were not actually being set because they used a nonexistent hash key
(which has the effect of unsetting the environment variable).

[mr-salty]

@haabaato PTAL - this makes the test pass but let me know if there's a better fix.

[haabaato]

Apologies for the delay as I'm currently attending a conference. 👍
Seems like a simple fix. Test was previously passing because NOT_FOUND_ERROR was being raised.

[mr-salty]

this was addressed more properly in #36 so closing this.

[haabaato]

@mr-salty #36 doesn't address this issue. Your PR seems fine to me.

[mr-salty]

argh, sorry, I read that too fast.

[tbetbetbe]

Is this still necessary ?

[mr-salty]

The test still fails for me without this change, so I think it's still needed.

[tbetbetbe]

Can you describe a bit more the environment where this test is failing; at the moment Travis is green ?

[tbetbetbe]

Ok, this is safe to add as it does not break the tests, and IUC, it breaks your other PR.

[mr-salty]

That is a good question about why it was failing for me locally but not failing in travis (which it clearly is not). I was using ruby 1.9 but that doesn't seem to be it, I also see the failure with 2.2. @haabaato - any thoughts?

FWIW, here is the (edited) log:

$ git checkout caed076711de9375772123560837975f118238fb
[...]
$ ruby --version
ruby 2.2.0p0 (2014-12-25 revision 49005) [x86_64-linux]
$ rvm --version
rvm 1.26.11 (latest) by Wayne E. Seguin <wayneeseguin@gmail.com>, Michal Papis <mpapis@gmail.com> [https://rvm.io/]
$ bundle --version
Bundler version 1.10.5
$ gem --version
2.4.6
$ bundle exec rake
[...]
Failures:

  1) #get_application_default when credential type is unknown fails if env vars are set
     Failure/Error: expect(&blk).to raise_error RuntimeError
       expected RuntimeError but nothing was raised
     # ./spec/googleauth/get_application_default_spec.rb:240:in `block (3 levels) in <top (required)>'

Finished in 6.48 seconds (files took 0.34353 seconds to load)
82 examples, 1 failure

Failed examples:

rspec ./spec/googleauth/get_application_default_spec.rb:234 # #get_application_default when credential type is unknown fails if env vars are set

[haabaato]

The test was always passing for me locally, but as I was trying to mention above, it was only passing because NOT_FOUND_ERROR is raised in get_application_default: https://github.com/google/google-auth-library-ruby/blob/master/lib/googleauth.rb#L116.
Though I had written the test assuming that read_creds would raise the error here: https://github.com/google/google-auth-library-ruby/blob/master/lib/googleauth.rb#L77

[mr-salty]

Ah, thanks - now I understand exactly what is happening. In my case it was picking up ~/.config/gcloud/application_default_credentials.json off the local disk and not throwing the exception. If I remove that file, then the test passes even without this PR.

Using fakefs everywhere (which Tim already opened as #40) would prevent that from happening. FWIW, I did try doing that (it's literally a 1-liner, 'require fakefs'), but there were some failures, so I went with a more narrow approach for my new tests. But, it's definitely a good idea. Maybe we can also do ENV.clear to prevent the user's environment from leaking in?