Variable being retained in unit test

Question

Created Oct ’20

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I'm having an interesting issue with unit testing a memory leak. I don't understand why the test fails when the line "context!.getView()" is uncommented, but we're suspecting it's a language intern issue. We can make the test pass as expected using an autorelease pool, but I don't understand the root cause of the problem.

The test:

Code Block class MemoryLeakTests: XCTestCase {
    func testExample() throws {
        var view:MockView?  = MockView()
        weak var weakRefToView = view
        var context: SomeContext? = SomeContext()
        context!.setView(view!)
        /* 
        Uncomment this and it fails 🤷‍♂️🤷‍♂️🤷‍♂️🤷‍♂️
        context!.getView()
        */
        
        view = nil
        XCTAssertNil(weakRefToView)
    }
}

Code Block @interface SomeContext : NSObject
- (MockView *) getView;
- (void) setView: (MockView*) view;
@end

Code Block #import "SomeContext.h"
@implementation SomeContext {
    __weak MockView* _view;
}
- (MockView*) getView {
    return _view;
}
- (void) setView: (MockView*) view {
    _view = view;
}
@end

Code Block #import <Foundation/Foundation.h>
NS_ASSUME_NONNULL_BEGIN
@interface MockView : NSObject
@end
NS_ASSUME_NONNULL_END

Code Block #import "MockView.h"
@implementation MockView
@end

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Answer 1

DTS Engineer OP

Apple

Oct ’20

We can make the test pass as expected using an autorelease pool

This doesn’t strike me as strange. ARC, as implemented by both Swift and Objective-C, may end up putting references to an object into the autorelease pool. If that happens, you won’t see that object deallocated until the autorelease pool is drained. In an XCTestCase method, the autorelease pool isn’t drained until return back into the XCTest infrastructure. If your unit test needs it to drain earlier, bracket that code with autoreleasepool { … }.

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