这样试试smth

class ViewController: UIViewController {
    var deinitCalled: (() -> Void)?
    deinit { deinitCalled?() }
}

class ViewControllerTest: XCTestCase {
    func test_deinit() { 
        var instance: ViewController? = ViewController()
        let exp = expectation(description: "Viewcontroller has deinited")
        instance?.deinitCalled = {
            exp.fulfill()
        }

        DispatchQueue.global(qos: .background).async {
            instance = nil
        }

        waitForExpectations(timeout: 2)
    }
}

I had the same problem.
When you examine the memory graph, you will see that an object of type UIStoryboardScene maintains a reference to your UIViewController via an @autorelease property ' sceneViewController '.
If you're unfamiliar with @autorelease, this is a helpful article: https://swiftrocks.com/autoreleasepool-in-swift . It explains that objects created with autorelease are released at the end of the current thread's run loop, but not before.
In Swift, we can use autoreleasepool to release UIStoryboardScene 's reference to the UIViewController.
It might look something like this:

var testViewController: UIViewController?
autoreleasepool {
    testViewController = UIStoryboard(name: "main", bundle: nil).instantiateInitialViewController()
}

Then, when you execute testViewController = nil , the UIViewController will actually deinit.

万一别人需要这个，我设法这样做。

// Given
    var optionalSubject: UIViewController? = UIViewController()

    // When
    optionalSubject = nil // Call deinit

    // Then
    // TEST DEINIT