Developer Tests - Things to Know

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 Kaunas JUG vaidas.pilkauskas@gmail.com
2. “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/
3. What I’m going to talk 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
5. “Legacy Code is code without Tests” Michael Feathers Working Effectively with Legacy Code
6. So what is test? It is system’s exercise under predefined conditions and then verification of an expected outcome.
7. Thing #1 Test phases
8. Test phases 1. Set up 2. Exercise 3. Verify 4. Tear down
9. Test phases @Test public void serverShouldExecuteJobSuccessfully() { Server server = new Server(); // set up Job job = new Job(); // set up Status status = server.execute(job); // exercise assertEquals(SUCCESS, status); // verify server.shutdown(); // tear down }
10. @Before public void before() { server = new Server(); } @Test public void serverShouldExecuteJobSuccessfully() { Job job = new Job(); // set up Status status = server.execute(job); // exercise assertEquals(SUCCESS, status); // verify server.shutdown(); // tear down }
11. @Before public void before() { server = new Server(); Job job = new Job(); } @Test public void serverShouldExecuteJobSuccessfully() { Status status = server.execute(job); // exercise assertEquals(SUCCESS, status); // verify server.shutdown(); // tear down }
12. @Test public void serverShouldQueueJobWithFutureDate() { // * set up which is actual for the current method // * use scope specific name Job futureJob = new Job(futureDate()); // set up Status status = server.execute(futureJob); // exercise assertEquals(SUCCESS, status); // verify server.shutdown(); // tear down }
13. @Before public void before() { server = new Server(); Job job = new Job(); } @Test public void serverShouldExecuteJobSuccessfully() { Status status = server.execute(job); // exercise assertEquals(SUCCESS, status); // verify } @After public void after() { server.shutdown(); // tear down }
14. @Before .. @Test public void serverShouldExecuteJobSuccessfully() { // * no need to name intermediate var, but // * may hide return meaning of server.execute() // execute & verify assertEquals(SUCCESS, server.execute(job)); } @After ..
15. Set up • DRY principle
16. Set up • DRY principle • Readability
17. Set up • DRY principle • Readability • Consistency
18. Set up • DRY principle • Readability • Consistency • Complexity
19. 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
20. Thing #2 What do we test?
21. Test behaviour not methods • Think of a contract
22. Test behaviour not methods • Think of a contract • And responsibilities
23. Test behaviour not methods • Think of a contract • And responsibilities • Specify requirements as tests
24. Test behaviour not methods • Think of a contract • And responsibilities • Specify requirements as tests • Happens naturally when done in test-first approach
25. Thing #3 Matchers
26. Matchers • Enhanced readability • Assertions on the right level of abstraction • Encapsulate testing logic • Reusable • Detailed match error messages (do not leave them out in your custom matchers!)
27. Matcher libraries • Hamcrest - standard matcher lib for JUnit • AssertJ - fluent assertions (IDE friendly) • Bring common matchers for you to use • Write your own custom matchers
28. Hamcrest assertThat(theBiscuit, equalTo(myBiscuit)); assertThat(theBiscuit, is(equalTo(myBiscuit))); assertThat(theBiscuit, is(myBiscuit));
29. AssertJ assertThat(frodo.getName()).isEqualTo("Frodo"); assertThat(frodo).isNotEqualTo(sauron) .isIn(fellowshipOfTheRing); assertThat(sauron).isNotIn(fellowshipOfTheRing);
30. Thing #4 Custom matchers
31. Custom matchers Are matchers we develop specifically for our projects
32. 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 custom message to be more specific about test failure
33. Custom matchers @Test public void testBookIsbn() { Book book = new Book(1l, "5555", "A book"); assertThat(book, hasIsbn("1234")); }
34. Thing #5 Failing test
35. fail() In some cases like testing exceptions you may want to force test to fail if some expected situation does not happen
36. fail() try{ // do stuff... fail("Exception not thrown"); }catch(Exception e){ assertTrue(e.hasSomeFlag()); }
37. 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
38. Thing #6 Anti-pattern: The Ugly Mirror
39. 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()); }
40. 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()); }
41. Anti-pattern: The Ugly Mirror @Test public void personToStringShouldIncludeNameAndSurname() { Person person = new Person("Vilkas", "Pilkas"); assertEquals("Person[Vilkas Pilkas]", person.toString()); }
42. Thing #7 How to turn off the test?
43. Why would you want to turn off the test? • Well, because it fails… :)
44. Ignoring tests • Always use ignore/pending API from your test library (JUnit @Ignore)
45. Ignoring tests • Always use ignore/pending API from your test library (JUnit @Ignore) • Do not comment out or false assert your test
46. 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
47. Thing #8 What to do with exceptions?
48. Exceptions • If you can, use matchers instead of ◦ @Test(expected=?)
49. 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]
50. Exceptions • If you can, use matchers instead of ◦ @Test(expected=?) ◦ try-catch approach
51. 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! } }
52. Exceptions • If you can, use matchers instead of ◦ @Test(expected=?) ◦ try-catch approach • catch-exception lib
53. catch-exception lib List myList = new ArrayList(); catchException(myList).get(1); assertThat(caughtException(), allOf( is(IndexOutOfBoundsException.class), hasMessage("Index: 1, Size: 0"), hasNoCause() ) );
54. Exceptions • If you can, use matchers instead of ◦ @Test(expected=?) ◦ try-catch approach • catch-exception lib • What about ExpectedException Rule? ◦ My personal opinion - not that intuitive ◦ breaks arrange/act/assert flow
55. 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); // ... }
56. Thing #9 How to test asynchronous code?
57. Asynchronous code • Do not Thread.sleep - makes test slow
58. Asynchronous code • Do not Thread.sleep - makes test slow • Use Awaitility, or similar DSL for synchronizing asynchronous operations
59. Awaitility (Java 8 example) @Test public void shouldPersistNewUser() { publish(new CreateUserCommand("Vilkas Pilkas")); await().until(userRepo::size, is(1)); //how long to await? (Default is 10 seconds) await().until(userRepo::isNotEmpty); }
60. Asynchronous code • Do not Thread.sleep - makes test slow • Use Awaitility, or similar DSL for synchronizing asynchronous operations • Use reasonable await time to avoid flaky tests
61. Thing #10 Testing with time
62. Problem public class MyService { ... public void process(LocalDate date) { if (date.isBefore(LocalDate.now()) { ... } } }
63. 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
64. Control time with Clock public class MyService { private Clock clock; // dependency inject ... public void process(LocalDate date) { if (date.isBefore(LocalDate.now(clock)) { ... } } }
65. Thing #11 Collections
66. Collections - multiple properties to assert • Is null? • Size • Order • Content
67. Collections • Most of the time you want to assert on collection content
68. Collections • Most of the time you want to assert on collection content • Prefer exact content matching
69. Collections • Most of the time you want to assert on collection content • Prefer exact content matching • Avoid incomplete assertions
70. 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!
71. 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
72. 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!
73. 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!
74. Thing #12 Access modifiers
75. Access modifiers • Rule is simple - never access anything that is not public in your tests
76. Access modifiers • Rule is simple - never access anything that is not public in your tests • Private things are implementation details which are not part of the public contract
77. Access modifiers • Rule is simple - never access anything that is not public in your tests • Private things are implementation details which are not part of the public contract • Same applies for protected/package modifiers. They must be there for production code, but not available to your tests
78. Thing #13 Random values
79. Random values in tests • Most of the time you do not want it
80. 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
81. 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)
82. 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
83. What if we still need random cases?
84. Generate Multiple Test Cases • Quality over quantity
85. Generate Multiple Test Cases • Quality over quantity • Think of boundary cases, that you may want to detect with random test
86. Generate Multiple Test Cases • Quality over quantity • Think of boundary cases, that you may want to detect with random test • Use parameterized tests
87. 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
88. 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
89. Thing #14 How many assertions per test?
90. How many assertions per test? • Unit test - one assertion per test. Must be clear and readable • Proper unit tests should fail for exactly one reason • End to end - best case one assertions per test, but more allowed • Consider custom matchers
91. Thing #15 Test Doubles
92. Test Doubles The name comes from the notion of a Stunt Double in movies
93. Why do we need test doubles? • To test in an isolated environment by replacing real collaborators with doubles • To have fast tests • To test interactions • To change collaborators behaviour in test
94. Types of Test Doubles • Dummy • Fake • Stub • Spy • Mock
95. Dummy Dummy objects are passed around but never actually used. Usually they are just used to fill parameter lists
96. Fake Fake objects actually have working implementations, but usually take some shortcut which makes them not suitable for production (an in memory database is a good example)
97. Stub Stubs provide canned answers to calls made during the test, usually not responding at all to anything outside what's programmed in for the test. Stubs may also record information about calls, such as an email gateway stub that remembers the messages it 'sent', or maybe only how many messages it 'sent'
98. Spy Stubs that verify behavior
99. Mock Mocks are what we are talking about here: objects pre-programmed with expectations which form a specification of the calls they are expected to receive
100. So what’s the difference between Spy and Mock?
101. Thing #16 Naming
102. Where to keep your tests • Recommendation: keep them in separate package from production code
103. Class Naming • End test classes with Test suffix (or one required by your test framework) • For long test classes: ◦ split by feature ◦ by input type
104. Method Naming • Everybody should follow the same pattern • testGeneratePassword vs shouldGenerateValidPassword
105. Naming Test Doubles • Intention revealing stubEngine, spyServer, dummyUser, mockService
106. Thing #17 Comments
107. 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 set up method (not the first thing to be seen in test method)
108. Thanks! Q & A