     XCTAssert(
       RxUIApplicationTestCase
       .statesFromCall {
-        $0.application(
+        $0.application!(
           UIApplication.shared,
           shouldSaveApplicationState: CoderStub(id: "x")
         )

  func testWillEnterBackground() {
    XCTAssertEqual(
      RxUIApplicationTestCase
      .statesFromCall { $0.applicationWillEnterForeground(UIApplication.shared) }
      .map { $0.session.state }
      ,
      [.currently(.awaitingLaunch), .pre(.active(.some))]

  func testDidBecomeActive() {
    XCTAssert(
      RxUIApplicationTestCase
      .statesFromCall { $0.applicationDidBecomeActive!(UIApplication.shared) }
      .map { $0.session.state }
      ==
      [.currently(.awaitingLaunch), .currently(.active(.some))]
