How can I get XCTest to wait for async calls in setUp before tests are run?

Question

I'm writing integration tests in Xcode 6 to go alongside my unit and functional tests. XCTest has a setUp() method that gets called before every test. Great!

It also has XCTestException's which let me write async tests. Also great!

However, I would like to populate my test database with test data before every test and setUp just starts executing tests before the async database call is done.

Is there a way to have setUp wait until my database is ready before it runs tests?

Here's an example of what I have do now. Since setUp returns before the database is done populating I have to duplicate a lot of test code every test:

func test_checkSomethingExists() {

    let expectation = expectationWithDescription("")
    var expected:DatabaseItem

    // Fill out a database with data. 
    var data = getData()
    overwriteDatabase(data, {
      // Database populated.
      // Do test... in this pseudocode I just check something...
      db.retrieveDatabaseItem({ expected in

        XCTAssertNotNil(expected)

        expectation.fulfill()
      })
    })

    waitForExpectationsWithTimeout(5.0) { (error) in
        if error != nil {
            XCTFail(error.localizedDescription)
        }
    }

}

Here's what I would like:

class MyTestCase: XCTestCase {

    override func setUp() {
        super.setUp()

        // Fill out a database with data. I can make this call do anything, here
        // it returns a block.
        var data = getData()
        db.overwriteDatabase(data, onDone: () -> () {

           // When database done, do something that causes setUp to end 
           // and start running tests

        })        
    }

    func test_checkSomethingExists() {

        let expectation = expectationWithDescription("")
        var expected:DatabaseItem


          // Do test... in this pseudocode I just check something...
          db.retrieveDatabaseItem({ expected in

            XCTAssertNotNil(expected)

            expectation.fulfill()
        })

        waitForExpectationsWithTimeout(5.0) { (error) in
            if error != nil {
                XCTFail(error.localizedDescription)
            }
        }

    }

}

Answer 1

There are two techniques for running asynchronous tests. XCTestExpectation and semaphores. In the case of doing something asynchronous in setUp, you should use the semaphore technique:

override func setUp() {
    super.setUp()

    // Fill out a database with data. I can make this call do anything, here
    // it returns a block.

    let data = getData()

    let semaphore = DispatchSemaphore(value: 0)

    db.overwriteDatabase(data) {

        // do some stuff

        semaphore.signal()
    }

    semaphore.wait()
}

Note, for that to work, this onDone block cannot run on the main thread (or else you'll deadlock).

---

If this onDone block runs on the main queue, you can use run loops:

override func setUp() {
    super.setUp()

    var finished = false

    // Fill out a database with data. I can make this call do anything, here
    // it returns a block.

    let data = getData()

    db.overwriteDatabase(data) {

        // do some stuff

        finished = true
    }

    while !finished {
        RunLoop.current.run(mode: .default, before: Date.distantFuture)
    }
}

This is a very inefficient pattern, but depending upon how overwriteDatabase was implemented, it might be necessary

Note, only use this pattern if you know that onDone block runs on the main thread (otherwise you'll have to do some synchronization of finished variable).