XCTest - Use custom notification center in test case and assert notification (not) triggered.

CustomNotificationCenterTestCase.swift

class CustomNotificationCenterTestCase: XCTestCase {

    var notificationCenter: NotificationCenter!

    override func setUp() {
        super.setUp()

        notificationCenter = NotificationCenter()
    }

    override func tearDown() {
        notificationCenter = nil

        super.tearDown()
    }

    func testTriggerNotification() {
        let notificationExpectation = XCTNSNotificationExpectation(name: .fooBar,
                                                                   object: nil,
                                                                   notificationCenter: notificationCenter)

        notificationCenter.post(name: .fooBar,
                                object: self)

        wait(for: [notificationExpectation], timeout: 0.1)
    }

    func testDidNotTriggerNotification() {
        let notificationExpectation = XCTNSNotificationExpectation(name: .fooBar,
                                                                   object: nil,
                                                                   notificationCenter: notificationCenter)
        notificationExpectation.isInverted = true

        // Run code that should not trigger a notification
        if false {
            notificationCenter.post(name: .fooBar,
                                    object: nil)
        }

        wait(for: [notificationExpectation], timeout: 0.1)
    }
}

extension Notification.Name {
    static let fooBar = Notification.Name(rawValue: "fooBar")
}

// Run tests in playground
CustomNotificationCenterTestCase.defaultTestSuite.run()