Unit test for checking for retain cycles in Swift. Replace `CLASS_YOU_WANT_TO_TEST` with your class name.

RetainCycleUnitTest.swift

func testCleanup() {

    // Extend your class inline in order to add closure property `deinitCalled`, 
    // which indicates when/if your class's deinit() gets called
    class ClassUnderTest: CLASS_YOU_WANT_TO_TEST {
        var deinitCalled: (() -> Void)?
        deinit { deinitCalled?() }
    }

    // Set up async expectation, which causes the test to wait for `deinitCalled` 
    // to be called
    let exp = expectation(description: "exp")
    
    // Initialize the class
    var instance: ClassUnderTest? = ClassUnderTest()

    // Set up up the `deinitCalled` closure, making the test succeed
    instance?.deinitCalled = {
        exp.fulfill()
    }

    // On a different queue, remove the instance from memory,
    // which should call `deinit`, in order to clean up resources.
    // If this doesn't cause `deinit` to be called, you probably have a
    // retain cycle
    DispatchQueue.global(qos: .background).async {
        instance = nil
    }

    // Wait for max. five seconds for the test to succeed, if not,
    // you may have a memory leak due to a retain cycle
    waitForExpectations(timeout: 5)
}