How to test DispatchQueue in Swift

Issue #646

Sync the DispatchQueue

Pass DispatchQueue and call queue.sync to sync all async works before asserting

Use mock

Use DispatchQueueType and in mock, call the work immediately

import Foundation

public protocol DispatchQueueType {
    func async(execute work: @escaping @convention(block) () -> Void)
}

extension DispatchQueue: DispatchQueueType {
    public func async(execute work: @escaping @convention(block) () -> Void) {
        async(group: nil, qos: .unspecified, flags: [], execute: work)
    }
}

final class MockDispatchQueue: DispatchQueueType {
    func async(execute work: @escaping @convention(block) () -> Void) {
        work()
    }
}