Unit Testing - Core Data - page 181

Testing performBlock() executions can be tricky since you need some way to signal
to “the outside world” from inside the block about the test status. Luckily, there are
new features in XCTestCase called expectations that help with this.
The example below shows how you might use an expectation to wait for an
asynchronous method to complete before finishing the test:
let expectation = self . expectationWithDescription ( "Done!" );
someService.callMethodWithCompletionHandler() {
expectation.fulfill()
}
self . waitForExpectationsWithTimeout ( 2.0 , handler: nil )
The key is that something must fulfill or trigger the expectation so the test moves
forward. The wait method at the end takes a time parameter (in seconds), so that
the test isn't waiting forever and can time out (and fail) in case the expectation is
never fulfilled.
In the example provided, you can see fulfill() is called explicitly in the
completion handler passed in to the tested method. With Core Data saves, it's
easier to listen for the NSManagedObjectDidSaveNotification , since it happens in a
place where you can't call fulfill() explicitly.
Add a new method to CamperServiceTests.swift to test that the root context is
getting saved when a new camper is added:
func testRootContextIsSavedAfterAddingCamper() {
//1
let expectRoot = self . expectationForNotification (
NSManagedObjectContextDidSaveNotification ,
object: coreDataStack . rootContext ) {
notification in
return true
}
//2
let camper = camperService . addCamper ( "Bacon Lover" ,
phoneNumber: "910-543-9000" )
//3
self . waitForExpectationsWithTimeout ( 2.0 ) {
error in
XCTAssertNil (error, "Save did not occur" )
}
}