     func testTwoRefTypeParams() {
 
         func twoReferenceTypes(first: ReferenceType, second: ReferenceType) -> ReferenceType {
-            return ReferenceType(value:first.value + second.value)
+            return ReferenceType(value: first.value + second.value)
         }
 
         let curried = curry(twoReferenceTypes)
-        let partiallyApplied = curried(ReferenceType(value:3))
-        let result = partiallyApplied(ReferenceType(value:6))
+        let partiallyApplied = curried(ReferenceType(value: 3))
+        let result = partiallyApplied(ReferenceType(value: 6))
 
         XCTAssertEqual(9, result.value)
     }


    func testDigitSumHelperFunction() {

        XCTAssertEqual(0, digitSum(of:0))
        XCTAssertEqual(1, digitSum(of:1))
        XCTAssertEqual(3, digitSum(of:2))
        XCTAssertEqual(6, digitSum(of:3))
        XCTAssertEqual(55, digitSum(of:10))
        XCTAssertEqual(153, digitSum(of:17))
    }

    func testTwoStringParams() {

        let curried = curry(three)
        let result = curried("a")(2)(3.0)

        XCTAssertEqual(digitSum(of: 3), result)
    }

    func testFourDistinctParams() {
