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BackstopException causes backstop process to hang indefinitely

See original GitHub issue

If we encounter a BackstopException for any reason, the whole process just hangs after throwing the exception. Makes it difficult to set it up for CI.

Setup clean environment, backstop default scenario

Reproduction I’ve added an evaluation with an undefined variable to onReady.js

module.exports = function (chromy, scenario, vp) {
  console.log('SCENARIO > ' + scenario.label);
  require('./clickAndHoverHelper')(chromy, scenario);
  // add more ready handlers here...

    chromy.evaluate(() => {
      IAmTotallyUndefined // will cause BackstopException -> undefined variable
    });
};

Error output

COMMAND | Command `reference` ended with an error after [1.416s]
COMMAND | BackstopException: BackstopJS Homepage on undefined: Error: An error has occurred evaluating the script in the browser.ReferenceError: IAmTotallyUndefined is not defined
    at result (<anonymous>:3:7)
    at <anonymous>:4:7

afterwards hanging forever until process is exited manually

Encountering TimeoutExceptions or other Exceptions correctly exits. Any idea where to start?

edit: for now i went with a bare bones approach of calling process.exit(1) in the promise.catch block after logging the error. Seems like a bad solution though. chrome instances are not properly shutdown.