https://stackoverflow.com/q/58573495/1271826

AsyncTest.swift

class MyAppTests: XCTestCase {
    func testIets() {
        let expectation = self.expectation(description: "doSomething")

        AsyncClass().doSomething {
            expectation.fulfill()
        }

        wait(for: [expectation], timeout: 5)
    }
}

class AsyncClass {
    func doSomething(completion: @escaping () -> Void) {
        let group = DispatchGroup()

        for _ in 0...5 {
            group.enter()

            DispatchQueue.global().async {
                Thread.sleep(forTimeInterval: 1)

                group.leave()
            }
        }

        group.notify(queue: .main) {
            completion()
        }
    }
}

In the end, I just wanted this:

func testIets() {
    var isCalled = false
    AsyncClass().doSomething()
    var isCalled = true

    XCTAssert(isCalled)
}

(ofcourse without the boolean isCalled). If you haven't seen it, I implemented this behavior: https://stackoverflow.com/a/58576029/7715250. As I explained it inside many comments, I want to fill my database with random data. Thats expensive CPU operation, so I want to dispatch it to all available threads, so not only the calling thread. I also want it sync, because I don't want to deal all the time with all the expectations and closures. If there is a better way, I would like to see how :)

@Jasperav - IMHO, it’s not advisable to introduce anti-patterns into one's codebase solely for the sake of testing, when the testing framework already provides a nice, concise mechanism to test these scenarios.

My suggestion is that you do not add blocking/synchronous methods to your code base, and instead use expectations when testing.