truizlop

func concat(first : String, second : String) -> String {
    switch (first, second) {
    case ("Another ", "example"): return "Another example"
    case ("Property-based ", "Testing"): return "Property-based Testing"
    case ("Swift ", "rocks"): return "Swift rocks"
    case ("One more ", "thing"): return "One more thing"
    default: return "Hello, World!"
    }
}

truizlop

func testStringConcat() {
    for _ in 0 ..< 100 {
        let a = randomString()
        let b = randomString()
        let expected = a + b
        XCTAssertEqual(expected, concat(first: a, second: b))
    }
}

truizlop

func testConcatLengthIsEqualToSumOfLengths() {
    for _ in 0 ..< 100 {
        let a = randomString()
        let b = randomString()
        let result = concat(first: a, second: b)
        XCTAssertEqual(result.length, a.length + b.length)
    }
}

truizlop

func testConcatIsAssociative() {
    for _ in 0 ..< 100 {
        let a = randomString()
        let b = randomString()
        let c = randomString()
        let result1 = concat(first: concat(first: a, second: b), second: c)
        let result2 = concat(first: a, second: concat(first: b, second: c))
        XCTAssertEqual(result1, result2)
    }
}

truizlop

func testConcatHasEmptyStringAsNeutralElement() {
    for _ in 0 ..< 100 {
        let a = randomString()
        let result = concat(first: a, second: "")
        XCTAssertEqual(result, a)
    }
}

truizlop

func testConcatLengthIsEqualToSumOfLengths() {
    property("Concatenation length is equal to sum of input lengths") <- forAll { (a : String, b : String) in
        let output = concat(first: a, second: b)
        return output.characters.count == a.characters.count + b.characters.count
    }
}

func testConcatIsAssociative() {
    property("Concatenation is associative") <- forAll { (a : String, b : String, c : String) in
        let output1 = concat(first: concat(first: a, second: b), second: c)

truizlop

property("Whatever property") <- forAll { (a : String) in 
  // Test property
}

truizlop

property("Whatever property") <- forAll(String.arbitrary) { (a : String) in
  // Test property
}

truizlop

let positiveIntsGen = Int.arbitrary.suchThat{ n in n > 0 }

truizlop

let uppercaseCharacterGen = Gen<Character>.fromElementsIn(Character("A")...Character("Z"))