testErrbacks() {
    /** @suppress {checkTypes} suppression added to enable type checking */
    const m = new ModuleInfo();
    m.setModuleConstructor(TestModule);
    let index = 0;
    let a = -1;
    let b = -1;
    let c = -1;
    const d = -1;

    const ca = m.registerErrback(() => {
      a = index++;
    });
    const cb = m.registerErrback(() => {
      b = index++;
    });
    const cc = m.registerErrback(() => {
      c = index++;
    });
    m.onError(/** @type {?} */ ('foo'));

    assertTrue('callback A should have fired', a >= 0);
    assertTrue('callback B should have fired', b >= 0);
    assertTrue('callback C should have fired', c >= 0);

    assertEquals('ordering of callbacks was wrong', 0, a);
    assertEquals('ordering of callbacks was wrong', 1, b);
    assertEquals('ordering of callbacks was wrong', 2, c);
  }
Tests the error callbacks. @suppress {checkTypes} suppression added to
     enable type checking