functions/billing: test failure with non-actionable messages

Two tests have this same failure state, which prevents effective triage.

1. The tests need to be fixed
2. The test needs to surface the underlying error.

Currently blocking merge on #1515

  functions/billing tests
    notifies Slack
      functions_billing_slack
        ✓ should notify Slack when budget is exceeded (868ms)
    disables billing
      functions_billing_stop
(node:61) UnhandledPromiseRejectionWarning: ChildProcessError: Command failed: functions-framework --target=notifySlack --signature-type=event --port 8080
 `functions-framework --target=notifySlack --signature-type=event --port 8080` (exited with error code null)
    at callback (/tmpfs/src/github/nodejs-docs-samples/functions/billing/node_modules/child-process-promise/lib/index.js:33:27)
    at ChildProcess.exithandler (child_process.js:288:5)
    at emitTwo (events.js:126:13)
    at ChildProcess.emit (events.js:214:7)
    at maybeClose (internal/child_process.js:915:16)
    at Process.ChildProcess._handle.onexit (internal/child_process.js:209:5)
(node:61) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:61) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
        1) should disable billing when budget is exceeded

[JustinBeckwith]

I think you’re looking for something like this:

const {GoogleAuth} = require('google-auth-library');
const auth = new GoogleAuth({
  scopes: [
    'https://www.googleapis.com/auth/cloud-billing',
    'https://www.googleapis.com/auth/cloud-platform',
  ],
});
google.options({auth});

[ace-n]

Closing as duplicate of #1988 (which was fixed just now anyway).