Let's just test that real quick

Property-based testing changes the way you look at your test suites. Instead of specifying test cases one after another, this advanced testing technique enables you to use logic to automatically generate a stream of inputs. Despite its potential, property-based testing still remains under the radar within the Java community. Let's try to uncover its strengths together.

The talk will discuss how property-based testing compares to traditional testing methods and demonstrate its principles with simple examples. We will also see how it fits into a TDD workflow and a CD pipeline. In order to bust the myth of the inapplicability of property-based testing in a real-world setting we'll bring up some use cases from industry. Finally, we'll wander into the world of concurrency and the automation of race condition detection.

As seen at Berlin Expert Days 2017.

Transcript

1. Let’s just test that Property-based testing
 in practice with Jan Stępień real quick
2. JAN STĘPIEŃ Senior Consultant jan.stepien@innoq.com Functional Programming Property-Based Testing Architecture and Development servus!
3. better at testing I want you to become
5. double stepsPerHour(int steps, double seconds) { return steps / (seconds * 60 * 60); }
6. assertThat(stepsPerHour(1, 2), equalTo(0.5)); assertThat(stepsPerHour(2, 2), equalTo(1)); assertThat(stepsPerHour(0, 3), equalTo(0)); @Test(expected = ArithmeticException.class) public void testZeroSeconds() { stepsPerHour(1, 0.0); }
7. [(1, 2, 0.5), (2, 2, 1), (0, 3, 0)].stream().map((steps, secs, value) B> { assertThat(stepsPerHour(steps, secs), equalTo(value)); });
8. ŏ ų = ŏ ų
9. ŏ ų = ŏ ų ŏ ų · ų = ŏ ų · ų
10. ŏ ų = ŏ ų ŏ ų · ų = ŏ ų · ų ŏ ų · ų = ŏ
11. [(1, 2, 0.5), (2, 2, 1), (0, 3, 0)].stream().map((steps, secs, value) B> { assertThat(stepsPerHour(steps, secs), equalTo(value)); });
12. [(1, 2), (2, 2), (0, 3)].stream().map((steps, secs) B> { assertThat(3600 * secs * stepsPerHour(steps, secs), equalTo(steps)); });
13. QuickCheck
15. junit-quickcheck github.com/pholser/junit-quickcheck
16. @RunWith(JUnitQuickcheck.class) public class StepsPerSecondProperties { @Property void stepsProperty(int steps, double secs) { assertThat(3600 * secs * stepsPerHour(steps, secs), equalTo(steps)); } }
17. QuickTheories github.com/ncredinburgh/QuickTheories
18. public class StepsTest { @Test public void stepsProp() { qt() .forAll(integers().allPositive(), doubles().any()) .checkAssert((steps, secs) B> assertThat( 3600 * secs * stepsPerHour(steps, secs), equalTo(steps))); } }
19. ------------------------------------------------------- T E S T S ------------------------------------------------------- Running cc.stepien.qc.StepsTest Tests run: 1, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 0.541 sec <<< FAILURE! stepsProp(cc.stepien.qc.StepsTest) Time elapsed: 0.426 sec <<< FAILURE! java.lang.AssertionError: Property falsified after 1 example(s) Smallest found falsifying value(s) S- {1, 0.0} Cause was S- java.lang.AssertionError: Expected: <1> but: was <NaN> at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18) at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:6) at cc.stepien.qc.StepsTest.lambda$stepsProp$0(StepsTest.java:16) ...
20. public class StepsTest { @Test public void stepsProp() { qt() .forAll(integers().allPositive(), doubles().any()) .checkAssert((steps, secs) B> assertThat( 3600 * secs * stepsPerHour(steps, secs), equalTo(steps))); } }
21. public class StepsTest { @Test public void stepsProp() { qt() .forAll(integers().allPositive(), doubles().any()) .assuming((steps, secs) B> secs != 0) .checkAssert((steps, secs) B> assertThat( 3600 * secs * stepsPerHour(steps, secs), equalTo(steps))); } }
22. ------------------------------------------------------- T E S T S ------------------------------------------------------- Running cc.stepien.qc.StepsTest Tests run: 1, Failures: 1, Errors: 0, Skipped: 0, Time elapsed: 0.62 sec <<< FAILURE! stepsProp(cc.stepien.qc.StepsTest) Time elapsed: 0.521 sec <<< FAILURE! java.lang.AssertionError: Property falsified after 1 example(s) Smallest found falsifying value(s) S- {1, 4.9E-324} Cause was S- java.lang.AssertionError: Expected: <1> but: was <Infinity> at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:18) at org.hamcrest.MatcherAssert.assertThat(MatcherAssert.java:6) at cc.stepien.qc.StepsTest.lambda$stepsProp$1(StepsTest.java:17) ...
23. int[] reverse(int[] array) { ... }
24. @RunWith(JUnitQuickcheck.class) public class ReverseProperties { @Property void reverseProperty(int[] array) { ... } }
25. @RunWith(JUnitQuickcheck.class) public class ReverseProperties { @Property void reverseProperty(int[] array) { assertThat(reverse(reverse(array)), equalTo(array)); } }
26. { name: "Orson Welles", cinematography: [ { title: "Citizen Kane”, year: 1941, director: { name: "Orson Welles" }, screenwriter: { name: "Orson Welles" }, starring: [ { name: "Orson Welles" }, { name: "Joseph Cotten" }, { name: "Dorothy Comingore" } ] } ] }
27. GET /hosen/lee/farbe-hellblau/40-70-euro/seite-2
28. perty-based testing
 ctice with Jan Stępień al quick wat
29. GET /hosen/lee/farbe-hellblau/40-70-euro/seite-2
30. GET /hosen/lee/farbe-hellblau/40-70-euro/seite-2 { category: "pants", brand: "lee", color: "light-blue", page: 2, price: { from: 40, to: 70 } }
31. State happens
32. RedisCache accompanied by an oracle java.util.HashMap
33. RedisCache accompanied by an oracle java.util.HashMap
34. RedisCache accompanied by an oracle java.util.HashMap
35. [“put”, “foo”, “bar”] [“clear”] [“put”, “foo”, “123”] [“get”, “foo”] [“count”]
36. Testing the Hard Stuff
 and Staying Sane John Hughes
37. [ α β γ δ ] [ 1 2 3 4 ] [ α β γ δ 1 2 3 4 ]
38. [ α β γ δ ] [ 1 2 3 4 ] [ α β γ δ 1 2 3 4 ]
39. [ α β γ δ ] [ 1 2 3 4 ] [ α β 1 2 3 4 γ δ ]
40. [ α β γ δ ] [ 1 2 3 4 ] [ α 1 β 2 γ 3 δ 4 ]
41. Jepsen: On the perils
 of network partitions Kyle “Aphyr” Kingsbury
42. better at testing I want you to become
43. Let’s just test that with Jan Stępień @janstepien — jan@stepien.cc real quick