Assertion that a promise-fn fails

assert-throws-async

const assert = require('assert');
const _ = require('lodash');

function throwsAsync(block, expectedError, message) {
	return block()
		.then(res => {
			assert.fail(res, expectedError, message, 'is');
		}, err => {
			if (_.isFunction(expectedError)) {
				// note that assert.throws doesn't work with custom Error constructors
				//https://github.com/nodejs/node/issues/3188
				return assert(err instanceof expectedError, `Expected error {${err.name}} to be instanceof ${expectedError.name}`);
			}
			assert.throws(() => { throw err; }, expectedError, message);
		});
}

module.exports = throwsAsync;