A sample for testing memory leaks

XCTAssertDeallocation.swift

// Adapted from https://www.avanderlee.com/swift/memory-leaks-unit-tests/

// --------------> Usage <-------------------
XCTAssertDeallocation(of: {
    MyViewController(...)
})

// With some setup:
XCTAssertDeallocation(of: { () -> MyViewController in
    let myViewController = MyViewController(...)
    // call any function
    return myViewController
})

// Can also be used with other types, not only view controller.

// --------------> Implementation <-------------------

import Foundation
import XCTest
@testable import Oasis

public func XCTAssertDeallocation<T: AnyObject>(
    of buildElement: () -> T,
    file: StaticString = #file,
    line: UInt = #line) {
    weak var weakReference: T?

    autoreleasepool {
        let element = buildElement()
        weakReference = element
        // If it's a UIViewController, we need to trigger viewDidLoad.
        if let viewController = element as? UIViewController {
            _ = viewController.view
        }
    }

    XCTWait(for: weakReference == nil, timeout: 3.0, description: "Memory leak in \(T.self)", file: file, line: line)
}

/// Checks for the callback to be the expected value within the given timeout.
///
/// - Parameters:
///   - condition: The condition to check for.
///   - timeout: The timeout in which the callback should return true.
///   - description: A string to display in the test log for this expectation, to help diagnose failures.
func XCTWait(
    for condition: @autoclosure @escaping () -> Bool,
    timeout: TimeInterval, description: String,
    file: StaticString = #file,
    line: UInt = #line) {
    let end = Date().addingTimeInterval(timeout)

    var value: Bool = false
    let closure: () -> Void = {
        value = condition()
    }

    while !value && 0 < end.timeIntervalSinceNow {
        if RunLoop.current.run(mode: RunLoop.Mode.default, before: Date(timeIntervalSinceNow: 0.002)) {
            Thread.sleep(forTimeInterval: 0.002)
        }
        closure()
    }

    closure()

    XCTAssertTrue(value, "➡️? Timed out waiting for condition to be true: \"\(description)\"", file: file, line: line)
}