fix(testing): defineReadonlyEventProperty only if its not yet on the …

[nivekcode]

We have a project that uses CDK for testing Angular components. Some components are wrappers around a third-party library. We have a case where we need to pass down an event to a third-party component and are out of control how many times preventDefault is called. Currently, our test suite fails due to the CDK if preventDefault is called multiple times.

On each preventDefault call the CDK tries to redefine the read-only Event Property defaultPrevented. In think that we should not fail on multiple preventDefault calls. From my point of view, it's not ideal to call preventDefault multiple times but also doesn't hurt.

This fix only tries to redefine defaultPrevented if it doesn't exist on the event.

[mmalerba]

Would it make sense to also move the call to originalPreventDefault up? That way non-IE browsers will never need to call defineReadonlyEventProperty

const result = originalPreventDefault();
if(!event.defaultPrevented) {
  defineReadonlyEventProperty(event, 'defaultPrevented', true);
}
return result;

[nivekcode]

@mmalerba yes. that sounds reasonable. will update the PR

[crisbeto]

How does your test fail if preventDefault is called multiple times? My assumption was that it should be possible, because we're passing in configurable into defineProperty.

[crisbeto]

Doesn't this mean that it could still fail if IE calls preventDefault multiple times?

[nivekcode]

No - If preventDefault is called then defaultPrevented is true and the property will not be redefined. As you said it would also work if we call it with configurable: true. By default configurable is false.

[devversion]

Since we'll drop IE11 support for v13, we can remove this hack anyway. Closing in favor of #23394. Thanks for the contribution, and sorry it was on the backburner for some while.

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