Generating tests with SwiftCheck

In this talk, I will share how to take advantage of property-based testing using SwiftCheck and use it to catch bugs even earlier than you do already.

Resources & more → https://github.com/akashivskyy/talks

Transcript

1. Generating tests with SwiftCheck Adrian Kashivskyy @ Netguru
2. How many of you use XCTest for testing?
3. How many of you use Quick for testing?
4. How many of you don’t write tests? 😏
5. No Tests 5% Quick 20% XCTest 75% Source: 20 most starred Swift repositories on GitHub Testing frameworks in top popular projects
6. override func setUp() { sut = Rectangle(width: 1, height: 2) } func testMultiplication() { sut.scale(by: 2) XCTAssertEqual(sut.width, 2) XCTAssertEqual(sut.height, 4) }
7. • Prove correctness of your code • Catch regressions during development • Find edge cases before your users do Good tests
8. override func setUp() { sut = Rectangle(width: 1, height: 2) } func testMultiplication() { sut.scale(by: 2) XCTAssertEqual(sut.width, 2) XCTAssertEqual(sut.height, 4) }
9. func testMultiplicationByZero() { sut.scale(by: 0) XCTAssertEqual(sut.width, 0) XCTAssertEqual(sut.height, 0) } func testMultiplicationByFraction() { sut.scale(by: 0.5) XCTAssertEqual(sut.width, 0.5) XCTAssertEqual(sut.height, 1) }
10. Such tests are limited to developer’s imagination
11. Let computers come up with test cases
13. They introduce d
 QuickCheck
14. allEqual x y z = x == y && y == z allEqual' x y z = 2 * x == y + z prop_st x y (z :: Int) = allEqual x y z == allEqual' x y z 
 
 prop_rev_rev :: Eq a => [a] -> Bool prop_rev_rev xs = reverse (reverse xs) == xs main = $quickCheckAll
15. SwiftCheck https://github.com/typelift/SwiftCheck
16. property("contains same elements as input") property("elements are in ascending order")
17. property("contains same elements as input") <- forAll { (a: ArrayOf<Int>) in } property("elements are in ascending order") <- forAll { (a: ArrayOf<Int>) in }
18. property("contains same elements as input") <- forAll { (a: ArrayOf<Int>) in a.getArray.sorted().counts() == a.getArray.counts() } property("elements are in ascending order") <- forAll { (a: ArrayOf<Int>) in a.getArray.sorted().elementsAreInAscendingOrder() }
19. • You write assertions about logical properties • SwiftCheck looks for a failing case • If found, SwiftCheck shrinks input to smallest reproducible value that causes failure Testing with SwiftCheck
20. Demo
21. • struct Gen<A> • protocol Arbitrary SwiftCheck building blocks
22. • Responsible for generating random inputs • Just a wrapper around a closure • Controls distirbution of values • Supports functional composition struct Gen<A>
23. • Denote which types can be generated • Responsible for shrinking • Has one requirement: a static variable of Gen protocol Arbitrary
24. Demo
25. QuickSwiftCheck https://github.com/akashivskyy/QuickSwiftCheck
26. • Round trip • Relation to other equivalent implementations • Relation to input Which properties to test?
27. Question time!
28. Thanks, have a great evening! 🍻