         XCTAssertEqual(intersection!.duration, 60 * 15)
     }
 
-    func test_intersection_zero_duration() {
+    func test_intersectionZeroDuration() {
         let date1 = dateWithString("2019-04-04 17:00:00 -0700")
         let date2 = dateWithString("2019-04-04 17:30:00 -0700")
         let dateInterval1 = DateInterval(start: date1, duration: 60 * 30)

        XCTAssertEqual(dateInterval2.compare(dateInterval1), .orderedSame)
    }
    
    func test_comparison_operators() {
        let date1 = dateWithString("2019-04-04 17:00:00 -0700")
        let date2 = dateWithString("2019-04-04 17:30:00 -0700")
        let dateInterval1 = DateInterval(start: date1, duration: 60)

class TestDateInterval: XCTestCase {
    static var allTests: [(String, (TestDateInterval) -> () throws -> Void)] {
        return [
            ("test_defaultConstructor", test_defaultConstructor),
            ("test_startEndConstructor", test_startEndConstructor),
            ("test_startDurationConstructor", test_startDurationConstructor),
            ("test_compareDifferentStarts", test_compareDifferentStarts),
            ("test_compareDifferentDurations", test_compareDifferentDurations),
            ("test_compareSame", test_compareSame),
            ("test_comparisonOperators", test_comparisonOperators),
            ("test_intersects", test_intersects),
            ("test_intersection", test_intersection),
            ("test_intersectionZeroDuration", test_intersectionZeroDuration),
            ("test_intersectionNil", test_intersectionNil),
            ("test_contains", test_contains),
            ("test_hashing", test_hashing),
        ]
    }

    func test_defaultConstructor() {
        let dateInterval = DateInterval()
        XCTAssertEqual(dateInterval.duration, 0)
    }
    
    func test_startEndConstructor() {
        let date1 = dateWithString("2019-04-04 17:09:23 -0700")
        let date2 = dateWithString("2019-04-04 18:09:23 -0700")
        let dateInterval = DateInterval(start: date1, end: date2)
        XCTAssertEqual(dateInterval.duration, 60 * 60)
    }

    func test_startDurationConstructor() {
        let date = dateWithString("2019-04-04 17:09:23 -0700")
        let dateInterval = DateInterval(start: date, duration: 60)
        XCTAssertEqual(dateInterval.duration, 60)
    }

    func test_compareDifferentStarts() {
        let date1 = dateWithString("2019-04-04 17:09:23 -0700")
        let date2 = dateWithString("2019-04-04 18:09:23 -0700")
        let dateInterval1 = DateInterval(start: date1, duration: 100)
