Throw assertion does not catch class constructor errors

[ejmurra]

Use case: An abstract class which implements member checking in the constructor.

Example:

class FeedAggregator {
  constructor({feedName, feedType}) {
    this.feedName = feedName;
    this.feedType = feedType;

    // Check for methods that must be implemented
    if (this.getItems === undefined) {
      throw new TypeError("Class must define a getItems method");
    }
  }
}

class BadAggregator extends FeedAggregator {
  constructor({feedName, feedType}) {
    super({feedName, feedType});
  }
}

test("Expect FeedAggregator to throw error when subclass has no getItems method", t => {
  t.throws(new BadAggregator({feedName: 'test', feedType: 'test'}), TypeError("Class must define a getItems method"))
});

Expected output:

1 passed

Actual output:

1 failed

  1. Expect FeedAggregator to throw error when subclass has no getItems method
  failed with "Class must define a getItems method"
      BadAggregator.FeedAggregator (FeedAggregator.js:11:13)
    new BadAggregator (FeedAggregator.js:16:7)
    Test.fn (FeedAggregator.js:23:12)

[jamestalmage]

You need to wrap any statement in a function. It's not possible for us to catch the Error otherwise.

For one liners like that, arrow functions are where it's at:

test("Expect FeedAggregator to throw error when subclass has no getItems method", t => {
  t.throws(
    () => new BadAggregator({feedName: 'test', feedType: 'test'}), 
    TypeError("Class must define a getItems method")
  );
});

[ejmurra]

Thanks.