Developer Tests - Things to Know (Vilnius JUG)

There are many great talks that discuss challenges developers face when writing software tests. In this talk let's look at test design problems that may seem to be simple but yet fundamentally important and often misunderstood even by experienced programmers.

Transcript

1. Developer Tests Things to Know Vaidas Pilkauskas 2014 Vilnius JUG vaidas.pilkauskas@gmail.com
2. me My hobbies • developer at Wix.com • main language - Scala • main professional interest - developer communities If there is time left after my hobbies • mountain bicycle rider, snowboarder • consumer of rock music, contemporary art, etc
3. me - how to contact me connect with me on LinkedIn http://lt.linkedin. com/pub/vaidas-pilkauskas/8/77/863/ add me on G+ https://www.google.com/+VaidasPilkauskas follow on Twitter @liucijus
4. “We couldn’t understand why people without technical knowledge had to tell programmers “what” to do and, furthermore, they had to supervise “how” programmers did it.” Cristian Rennella http://qz.com/260846/why-our-startup-has-no-bosses-no-office-and-a-four-day-work-week/
5. What this talk is about • Things we argue about during code reviews • Things that took me time to understand and prove that they are actually good way to go • Small things we have no time to discuss during big talks
7. “Legacy Code is code without Tests” Michael Feathers Working Effectively with Legacy Code
8. So what is test? It is system’s exercise under predefined conditions and then verification of an expected outcome.
9. Thing #1 Test structure
10. Test phases Setup Exercise Verify Teardown
11. Test phases in code Server server = new NotesServer(); // setup Note note = new Note("test note"); // setup Status status = server.add(note); // exercise assertEquals(SUCCESS, status); // verify server.shutdown(); // teardown
12. Start everything in one method @Test public void serverShouldAddNoteSuccessfully() { Server server = new NotesServer(); // setup Note note = new Note("test note"); // setup Status status = server.add(note); // exercise assertEquals(SUCCESS, status); // verify server.shutdown(); // teardown }
13. Refactor to lifecycle methods @Before public void before() { server = new NotesServer(); // setup note = new Note("test note"); // setup } @Test public void serverShouldAddNoteSuccessfully() { Status status = server.add(note); // exercise assertEquals(SUCCESS, status); // verify } @After public void after() { server.shutdown(); // teardown }
14. DON’Ts - #1 Do not start from setup/teardown
15. DON’Ts - #2 Do not mix setup code from different tests - shared code must be relevant to the tests that use it
16. DON’Ts - #3 Setup and teardown are there to solve DRY problem and to help structure your test code
17. How many colors are there in the picture? Source: Josef Albers Interaction of Color
18. Context matters! Source: Josef Albers Interaction of Color
19. Typical setup inside @Before @Before public void before() { server = new NotesServer(); // setup note = new Note("test note"); // setup } @Test public void serverShouldAddNoteSuccessfully() { Status status = server.add(note); // exercise assertEquals(SUCCESS, status); // verify } @After public void after() { server.shutdown(); // teardown }
20. Setup pollution - #1 • Every line in setup must be relevant to all tests.
21. Setup pollution - #2 • It is tempting to add additional setup tuning just to fix/enhance one test.
22. Setup pollution - #3 • Rich setup makes tests slow!
23. Setup pollution - #4 • Setup is to bootstrap your SUT.
24. Setup pollution - #5 • Setup hides details! Do not hide test preconditions.
25. Setting up “job” inside test method @Before public void before() { server = new NotesServer(); // setup } @Test public void serverShouldAddNoteSuccessfully() { note = new Note("test note"); // setup Status status = server.add(note); // exercise assertEquals(SUCCESS, status); // verify }
26. But then be more specific @Test public void serverShouldAddSingleLineNoteSuccesfully() { // * set up which is actual for the current method // * use scope specific name Note singleLineNote = new Note("test note"); // setup Status status = server.add(singleLineNote); // exercise assertEquals(SUCCESS, status); // verify }
27. Give good names to setup methods @Before public void createNotesServer() { server = new NotesServer(); }
28. Summary of test code organization • DRY principle. • Readability. BDD vs. DRY • Consistency. Maintain the same style across your codebase. • Complexity. It may dictate the way you go.
29. Refactoring Refactoring is about improving the design of existing code. It is the process of changing a software system in such a way that it does not alter the external behavior of the code, yet improves its internal structure. Martin Fowler Refactoring: Improving the Design of Existing Code
30. Thing #2 What do we test?
31. Test behaviour not methods • Think of a contract
32. Test behaviour not methods • Think of a contract • And responsibilities
33. Test behaviour not methods • Think of a contract • And responsibilities • Specify requirements as tests
34. Test behaviour not methods • Think of a contract • And responsibilities • Specify requirements as tests • Happens naturally when done in test-first approach
35. Thing #3 Matchers
36. Matchers • Enhance readability • Asserts on the right level of abstraction • Encapsulate testing logic • Reusable • Detailed match error messages (do not leave them out in your custom matchers!)
37. Matchers • Enhance readability • Asserts on the right level of abstraction • Encapsulate testing logic • Reusable • Detailed match error messages (do not leave them out in your custom matchers!)
38. Matcher libraries • Hamcrest - standard matcher lib for JUnit • AssertJ - fluent assertions (IDE friendly) • Provides common matchers • You can write your own custom matchers
39. Hamcrest assertThat(frodo.getName(), equalTo("Frodo")); assertThat(frodo.getName(), is(equalTo("Frodo"))); assertThat(frodo.getName(), is("Frodo"));
40. AssertJ assertThat(frodo.getName()).isEqualTo("Frodo"); assertThat(frodo).isNotEqualTo(sauron).isIn(fellowshipOfTheRing); assertThat(sauron).isNotIn(fellowshipOfTheRing);
41. Thing #4 Custom matchers
42. Custom matchers Are matchers that we write specifically for our projects.
43. Custom matchers • Help communicate test intention • Abstract assertion logic in case standard matchers are not enough • Are reusable and save time in large projects • You may have a custom message to be more specific about test failure
44. Custom matchers • Help communicate test intention • Abstract assertion logic in case standard matchers are not enough • Are reusable and save time in large projects • You may have a custom message to be more specific about test failure
45. Custom matchers @Test public void shouldHaveIsbnGenerated() { Book book = new Book(1l, "5555", "A book"); assertThat(book, hasIsbn("1234")); }
46. Thing #5 Failing a test
47. fail() In some cases (e.g. testing exceptions) you may want to force test to fail if some expected situation does not happen
48. fail() try { // do stuff... fail("Exception not thrown"); } catch(Exception e){ assertTrue(e.hasSomeFlag()); }
49. fail() • Fundamentally not bad, but better use matchers for expected failure • Matchers help to clarify test intention • Don’t forget - expected behaviour is an opposite of a failing test
50. Thing #6 Anti-pattern: The Ugly Mirror
51. Anti-pattern: The Ugly Mirror @Test public void personToStringShouldIncludeNameAndSurname() { Person person = new Person("Vilkas", "Pilkas"); String expected = "Person[" + person.getName() + " " + person.getSurname() + "]" assertEquals(expected, person.toString()); }
52. Anti-pattern: The Ugly Mirror @Test public void personToStringShouldIncludeNameAndSurname() { Person person = new Person("Vilkas", "Pilkas"); String expected = "Person[" + person.getName() + " " + person.getSurname() + "]" assertEquals(expected, person. toString()); }
53. Anti-pattern: The Ugly Mirror @Test public void personToStringShouldIncludeNameAndSurname() { Person person = new Person("Vilkas", "Pilkas"); assertEquals("Person[Vilkas Pilkas]", person.toString()); }
54. Thing #7 How to turn off the test?
55. Why would you want to turn off the test?
56. Why would you want to turn off the test? Well, because it fails… :)
57. Ignoring tests • Always use ignore/pending API from your test library (JUnit @Ignore)
58. Ignoring tests • Always use ignore/pending API from your test library (JUnit @Ignore) • Do not comment out or false assert your test
59. Ignoring tests • Always use ignore/pending API from your test library (JUnit @Ignore) • Do not comment out or false assert your test • If you do not need a test - delete it
60. Thing #8 What to do with exceptions?
61. Exceptions • If you can, use matchers instead of ◦ @Test(expected=?) ◦ try-catch approach
62. JUnit expected exception @Test(expected=IndexOutOfBoundsException.class) public void shouldThrowIndexOutOfBoundsException() { ArrayList emptyList = new ArrayList(); Object o = emptyList.get(0); } //matcher in Specs2 (Scala) server.process(None) must throwA[NothingToProccess]
63. try and catch public void shouldThrowIndexOutOfBoundsException() { ArrayList emptyList = new ArrayList(); try { Object o = emptyList.get(0); fail("Should throw IndexOutOfBoundsException"); } catch(IndexOutOfBoundsException e)){ //consider asserting message! } }
64. Exceptions • catch-exception lib
65. catch-exception lib List myList = new ArrayList(); catchException(myList).get(1); assertThat(caughtException(), allOf( is(IndexOutOfBoundsException.class), hasMessage("Index: 1, Size: 0"), hasNoCause() ) );
66. Exceptions • What about ExpectedException Rule? ◦ My personal opinion - not that intuitive ◦ breaks arrange/act/assert flow
67. ExpectedException rule @Rule public ExpectedException exception = ExpectedException.none(); @Test public void testExpectedException() { exception.expect(IllegalArgumentException.class); exception.expectMessage(containsString('Invalid age')); new Person('Vilkas', -1); } //Person constructor public Person(String name, int age) { if (age <= 0) throw new IllegalArgumentException('Invalid age:' + age); // ... }
68. Thing #9 Testing with time
69. Problem public class MyService { ... public void process(LocalDate date) { if (date.isBefore(LocalDate.now()) { ... } } }
70. Testing with Time • Design your system where time is a collaborator • Inject test specific time provider in your test ◦ constant time ◦ slow time ◦ boundary cases time
71. Control time with Clock public class MyService { private Clock clock; // dependency inject ... public void process(LocalDate date) { if (date.isBefore(LocalDate.now(clock)) { ... } } }
72. Thing #10 Collections
73. Collections - multiple properties to assert • Is null? • Size • Order • Content
74. Collections • Most of the time you want to assert on collection content
75. Collections • Most of the time you want to assert on collection content • Prefer exact content matching
76. Collections • Most of the time you want to assert on collection content • Prefer exact content matching • Avoid incomplete assertions
77. Collections • Most of the time you want to assert on collection content • Prefer exact content matching • Avoid incomplete assertions • Do not sort just because it is easier to assert!
78. Collections • Most of the time you want to assert on collection content • Prefer exact content matching • Avoid incomplete assertions • Do not sort just because it is easier to assert! • Multiple assertions are worse than single content assertion
79. Collections • Most of the time you want to assert on collection content • Prefer exact content matching • Avoid incomplete assertions • Do not sort just because it is easier to assert! • Multiple assertions are worse than single content assertion • Unless you want to say something important in your test!
80. Collections • Most of the time you want to assert on collection content • Prefer exact content matching • Avoid incomplete assertions • Do not sort just because it is easier to assert! • Multiple assertions are worse than single content assertion • Unless you want to say something important in your test! • Use matchers!
81. Collections • Most of the time you want to assert on collection content • Prefer exact content matching • Avoid incomplete assertions • Do not sort just because it is easier to assert! • Multiple assertions are worse than single content assertion • Unless you want to say something important in your test! • Use matchers!
82. Thing #11 Random values
83. Random values in tests • Most of the time you do not want it
84. Random values in tests • Most of the time you do not want it • Unless you depend on randomness a lot (eg. password generation*) *Thanks to Aleksandar Tomovski for a good example
85. Random values in tests • Most of the time you do not want it • Unless you depend on randomness a lot • Use property based testing (which is also hard)
86. Random values in tests • Most of the time you do not want it • Unless you depend on randomness a lot • Use property based testing (which is also hard) • Do not make dummy values random
87. What if we still need random cases?
88. Generate Multiple Test Cases • Quality over quantity
89. Generate Multiple Test Cases • Quality over quantity • Think of boundary cases, that you may want to detect with random test
90. Generate Multiple Test Cases • Quality over quantity • Think of boundary cases, that you may want to detect with random test • Use parameterized tests
91. Generate Multiple Test Cases • Quality over quantity • Think of boundary cases, that you may want to detect with random test • Use parameterized tests • Random is hard to repeat
92. Generate Multiple Test Cases • Quality over quantity • Think of boundary cases, that you may want to detect with random test • Use parameterized tests • Random is hard to repeat • Flickering tests
93. Thing #12 How many assertions per test?
94. How many assertions per test? • Unit test - one assertion per test. Must be clear and readable • Proper test should fail for exactly one reason • End to end - best case one assertion per test, but more are allowed • Consider custom matchers
95. How many assertions per test? • Unit test - one assertion per test. Must be clear and readable • Proper test should fail for exactly one reason • End to end - best case one assertion per test, but more are allowed • Consider custom matchers
96. Thing #13 Decoupling in End-to-end tests
97. What can be better in this test [pseudocode] @Test shouldRetrieveUserByLogin() { String userJson = "{\"username\": \"vaidas\"}"; HttpRequest post = new Post("https://localhost:8080/users", userJson); HttpResponse postResp = HttpClient().execute(post); assertThat(postResp.status, is(200)); HttpRequest get = new Get("https://localhost:8080/users/vaidas"); HttpResponse getResp = HttpClient().execute(get); User user = mapper.readValue(getResp, User.class); assertThat(username, is("vaidas")); }
98. Decoupling from low level details [pseudocode] @Test shouldRetrieveUserByUsername() { CreateUserResponse createResp = aCreateUserRequest().withUsername("vaidas").execute(); assertThat(createResp, hasStatus(OK)); GetUserResponse getResp = aGetUserRequest().withUsername("vaidas").execute(); assertThat(getResp, allOf(hasStatus(OK), hasUsername("vaidas"))); }
99. Thoughts on end-to-end testing • What is real e2e? REST vs. UI • Testing by using system itself • Vs. using low level DB driver to verify data persistence
100. Thing #14 Comments
101. Comments in Test code • Fundamentally good option to explain complicated parts, but: • better use good method naming • custom matcher • do less, so that intention is clear • comments are not so bad in isolated well named methods
102. Summary • Context matters • Tests are controversial topic • And very opinionated
103. Thanks! Q & A