Using more mocks in implicit environ tests.

[dhermes]

This was done mostly because the GCE environment check was taking too long to time-out.

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Discovered while investigating #357.

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Currently, the four updated tests run in:

$ nosetests \
>   tests/test_client.py:GoogleCredentialsTests.test_get_adc_from_environment_variable_service_account \
>   tests/test_client.py:GoogleCredentialsTests.test_get_adc_from_environment_variable_authorized_user \
>   tests/test_client.py:GoogleCredentialsTests.test_get_adc_from_environment_variable_malformed_file \
>   tests/test_client.py:GoogleCredentialsTests.test_get_application_default_environment_not_set_up
....
----------------------------------------------------------------------
Ran 4 tests in 1.004s

OK

and after this update:

$ nosetests \
>   tests/test_client.py:GoogleCredentialsTests.test_get_adc_from_environment_variable_service_account \
>   tests/test_client.py:GoogleCredentialsTests.test_get_adc_from_environment_variable_authorized_user \
>   tests/test_client.py:GoogleCredentialsTests.test_get_adc_from_environment_variable_malformed_file \
>   tests/test_client.py:GoogleCredentialsTests.test_get_application_default_environment_not_set_up
....
----------------------------------------------------------------------
Ran 4 tests in 0.005s

OK

[nathanielmanistaatgoogle]

Don't the tests now run faster because they're executing less code? It looks like without this change the tests go all the way "through" oauth2client and hit the "test circumstances" "below" oauth2client, but with this change the mocking is done within oauth2client and the tests execute less production code than before.

Sorry for all the weird quotes; I don't talk about this sort of thing often so I don't have a strong vocabulary of concepts for it.

Since I know you're minding test coverage I know that you haven't uncovered any production code, but isn't there an argument to be made for redundant and overlapping test coverage?

How easily could I propose a guideline that oauth2client's tests should never mock out any part of oauth2client? One should never mock out any part of the system under test, right? So then it becomes a philosophical question of the extent to which test_module.py tests module.py and the extent to which it tests oauth2client, right?

[dhermes]

tests should never mock out any part of oauth2client

I disagree. There should be dedicated places to test a function, class or method. If another function, class or method relies on an already tested component, there is no need to re-test that part. Especially in cases where we go 3 or 4 layers deep. At that point, the mocks could begin to be larger than the actual testing code (or even the code under test).

[nathanielmanistaatgoogle]

I'd like to persuade you otherwise at some point but won't make an obstacle of it today. :-) Merging.

[dhermes]

Thanks.