Run tests with --throw-deprecations

[ofrobots]

Similar to #2839, it would be good for Google Cloud libraries to not use deprecated Node.js APIs. Deprecation messages printed to the console, however, can be easy to miss.

We should run tests with --throw-deprecations to ensure that use of deprecated APIs is caught by tests.

The same deprecation mechanism would work for our own deprecations, e.g. googleapis/google-auth-library-nodejs#402.

[JustinBeckwith]

Should we run all of our tests with this turned on, or just the system-tests and samples tests? I ask because we have unit tests that verify the warning behavior for deprecated APIs :)

[ofrobots]

We have unit tests that verify the warning behavior of all deprecations, including Node.js? Can you point me to how this is done?

[JustinBeckwith]

I was referring to this:
https://github.com/google/google-auth-library-nodejs/pull/402/files#diff-86629eb1fa03b5146081c8eed046735bR1407

When you run that unit test, it will emit the deprecation warning to the console.

[ofrobots]

Oh gotcha! In that test could you install a mock on process.emitWarning instead of installing a listener and expecting it to be called?

[JustinBeckwith]

All of the PRs for this have been submitted. Just waiting on fix in gax-nodejs to land the stragglers :)