Fix FlutterMetalLayer testDealloc flakiness on iOS 18

[knopp]

Fixes flutter/flutter#152990

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[jmagman]

Would something like this work (I didn't try it):

@interface FlutterMetalLayerTest : XCTestCase
@property(weak) FlutterMetalLayer *weakLayer;
@end

- (void)testDealloc {
  @autoreleasepool {
...
    self.weakLayer = layer;
...
  }
  XCTestExpectation *weakNil = [self keyValueObservingExpectationForObject:self keyPath:@"weakLayer" expectedValue:nil];
  [self waitForExpectationsWithTimeout:1.0 handler:nil];

[jmagman]

(I'm not sure about the KVO part, but it would be nice to let -waitForExpectations handle the runloop spinning.

[knopp]

@jmagman, I don't think KVO will work since zeroing weak reference doesn't trigger KVO notifications. I tried this

- (void)testDealloc {
   __weak FlutterMetalLayer* weakLayer;
  @autoreleasepool {
    FlutterMetalLayer* layer = [self addMetalLayer];
    weakLayer = layer;
    TestCompositor* compositor = [[TestCompositor alloc] initWithLayer:layer];

    id<CAMetalDrawable> drawable = [layer nextDrawable];
    BAIL_IF_NO_DRAWABLE(drawable);
    [drawable present];
    [compositor commitTransaction];

    [self removeMetalLayer:layer];
  }
  NSPredicate* predicate =
      [NSPredicate predicateWithBlock:^(id evaluatedObject, NSDictionary* bindings) {
        return weakLayer == nil;
      }];
  [self expectationForPredicate:predicate evaluatedWithObject:self handler:nil];
  [self waitForExpectationsWithTimeout:1 handler:nil];
}

Unfortunately it didn't work either. I can confirm that weakLayer==nil is YES in the predicate and yet the expection fails. Maybe I'm holding it wrong but I'm not sure how.

[jmagman]

since zeroing weak reference doesn't trigger KVO notifications

That's what I suspected, but I couldn't think other another way. Thanks for checking.

[flutteractionsbot]

Failed to create CP due to merge conflicts.
You will need to create the PR manually. See the cherrypick wiki for more info.

[knopp]

The fix that this test is for has not been cherry-pick, so I don't think this test should be either. FlutterMetalLayer is not enabled by default in stable.

[jmagman]

The fix that this test is for has not been cherry-pick, so I don't think this test should be either. FlutterMetalLayer is not enabled by default in stable.

Ha yeah, I remembered after the bot failed. Thanks!