[XCTestExpectation] Adding expectationForPredicate constructor

[minoltax700]

What's in this pull request?

This pull request adds the XCTestCase convenience constructor for XCTestExpectation expectation(forPredicate:evaluatedWithObject:handler:).

I added XCPredicateExpectation, an internal subclass of XCTestExpectation, to keep the evaluation logic separated (and to match the obj-c implementation). The re-evaluation interval has been shorted to 0.01 whereas the obj-c interval is about once per second.

This also includes a separate file for the typealias XCPredicateExpectationHandler.

There are tests for the expectation and the handler. Let me know if you think there should be more tests, I'd be happy to add other ideas.

https://bugs.swift.org/browse/SR-1110

Why merge this pull request?

This will provide a full Swift implementation of expectationForPredicate:evaluatedWithObject:handler: that allows asynchronous testing for NSPredicate.

[modocache]

With #94 merged you may now indent the // CHECK:, like so:

func myFunc() {
    // CHECK: foo
    print("foo")
    if (bar) {
        // CHECK: baz
        print("baz")
    }
}

I think indenting is more readable, so I'd encourage you to do that! (I had been meaning to start sending out pull requests to indent the checks in the tests, but forgot 😇 )

[modocache]

This is really excellent work, @yoonapps, thank you!!

@mike-ferris-apple Could you ask @swift-ci to please test?

[minoltax700]

@modocache Addressed reviews! I lowered the interval to 0.01 and updated the tests to wait for only 0.1.

[ddunbar]

@swift-ci please test

[briancroom]

I think the precise signature of this method needs to be adjusted. I'm seeing the following imported signature in Xcode using the latest Swift toolchain:

public func expectation(for predicate: NSPredicate, evaluatedWith object: AnyObject, handler: XCPredicateExpectationHandler? = nil) -> XCTestExpectation

Does this look right? @mike-ferris-apple @modocache

[modocache]

Agreed. This was generated with the Swift 3 importer from a month ago, but it matches @briancroom's signature.

[briancroom]

Excited to see this come in @yoonapps, thanks! I just left a couple questions.

[minoltax700]

I'm learning so much every PR! It's awesome.
@briancroom Thank you for fixing the strong reference issue in the expectationForNotification! I applied a similar fix here. I use weak self for networking a whole bunch at work. Such a "duh" moment. 😆
One question, I was going to fix the signature for init of XCPredicateExpectation as well but it looked like inits don't follow the same rules. Is that right?

[minoltax700]

I've tried CTRL + I here but this is where the indentation goes. Does this look funky or is it just me?

[modocache]

Yes, it does look strange. Personally, I would remove four spaces, in order to align it with the open brace on the self.timer = NSTimer.scheduledTimer(self.evaluationInterval, repeats: true, fire: { line. It's up to you, though! :)

[modocache]

One question, I was going to fix the signature for init of XCPredicateExpectation as well but it looked like inits don't follow the same rules.

Good observation! Apple XCTest doesn't provide a public initializer for XCTestExpectation, nor does it provide a public definition of any of its private subclasses (such as _XCPredicateExpectation). So we don't need to worry about providing an identical signature: no users of Apple XCTest should ever initialize an XCTestExpectation directly.

[minoltax700]

Gotcha! Is there anything else that needs to be addressed?

[modocache]

@briancroom does the timer invalidation look good?

@mike-ferris-apple Could you ask @swift-ci to please test?

[ddunbar]

@swift-ci please test

[briancroom]

Looks great! Nice work @yoonapps

[briancroom]

Actually, just one more thing - can we make this subclass have internal visibility, and return the base class type from the factory method on XCTestCase?

[minoltax700]

@briancroom Ah!! I had it internal initially but changed to public because of the factory method return type. I didn't realize that I could just return the base type! 😱💥 Mind blown.

[modocache]

Excellent, thanks @yoonapps!! That's two tasks under your belt! 💯

[minoltax700]

Not a problem. The experience I'm getting from these tasks are invaluable. Thanks for sending this task my way, @modocache! I'm always ready for more so let me know if you have any suggestions.