test: fix re-use existing authClient test

[ofrobots]

I believe this got broken by #21.

[stephenplusplus]

Can you explain more how this was broken? It also doesn't seem like the test that's been changed is still testing what it says it is (re-using a cached auth client).

[ofrobots]

With #21, if an authClient exists, we simply return it. The test was mocking authClient but and expecting authClientPromise would resolve to the mocked value of authClient.

[stephenplusplus]

Is this line tested anywhere?

google-auto-auth/index.js

Line 111 in ac4daa6

this.authClientPromise = Promise.resolve(this.authClient);

[ofrobots]

Not only was that line untested, it was unreachable. PTAL.

[ofrobots]

Actually it still might benefit from an additional test. Adding.