     }
     
     func testFirst_someData() {
-        XCTAssertEqual(try! Observable.of(42, 43, 44, 45).toBlocking().first(), 42)
+        XCTAssertEqual(try Observable.of(42, 43, 44, 45).toBlocking().first(), 42)
     }
     
     func testFirst_withRealScheduler() {

    }
    
    func testLast_someData() {
        XCTAssertEqual(try! Observable.of(42, 43, 44, 45).toBlocking().last(), 45)
    }
    
    func testLast_withRealScheduler() {

    }
    
    func testSingle_return() {
        XCTAssertEqual(try Observable.just(42).toBlocking().single(), 42)
    }

    func testSingle_two() {
