Unit Testing like a Pro - The Circle of Purity
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Best practices on designing unit tests, designing testable production code, a glimpse of TDD, using mocks and isolating pure functions for easy testing. Talk distilled from http://victorrentea.ro/#unit-testing Held at VoxxedDays Bucharest in March 2019.
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Unit Testing like a Pro - The Circle of Purity
- 1. VictorRentea.ro The Art of Unit Testing The Circle of Purity VictorRentea.ro Independent Trainer Lead Architect at IBM
- 2. When something is painful but you can't avoid doing it… postpone it
- 3. When something is painful but you can't avoid doing it… delegate it
- 4. When something is painful but you can't avoid doing it… Do It More Often! "Bring The Pain Forward!"
- 5. Continuous Integration Pair Programming Continuous Refactoring TDD XP "Bring The Pain Forward!"
- 7. Victor Rentea 14 years of Java Clean Code Evangelist VictorRentea.ro 30+ talks, 12 meetups .NET Lead Architect Tech Team Lead and Consultant Software Craftsman XP: Pair Programming, Refactoring, TDD
- 8. VictorRentea.ro @victorrentea victor.rentea@gmail.com Independent Technical Trainer & Coach HibernateSpring Java 8 Architecture, DDDDesign Patterns Clean Code Unit Testing, TDD Java Performance and much more…Scala 180+ days1300 devs6 years VictorRentea.rovictor.rentea@gmail.com 30 companies Posting daily on
- 14. VictorRentea.ro ▪Test Design Principles ▪TDD ▪Mocks ▪Databases ▪Legacy Code Agenda 15
- 15. VictorRentea.ro ▪Arrange: setup the test fixture ▪Act: call the production code ▪Assert the outcomes ▪Annihilate[opt]: clean up Terms 16 Professional Unit Testing – Basics
- 16. VictorRentea.ro Why do we Write Tests ? 17
- 17. VictorRentea.ro Full: https://www.youtube.com/watch?v=GvAzrC6-spQ Why do we Write Tests ? 18 Professional Unit Testing – Basics Uncle Bob on TDD Shorter: https://youtu.be/GvAzrC6-spQ?t=116 1:48
- 18. VictorRentea.ro19 Professional Unit Testing – Intro To Read-the-Spec™ (before we finish the implem☺) Why do we Write Tests ? FEAR
- 19. VictorRentea.ro Medical Screening 20 Professional Unit Testing – Principles of Test Design
- 20. VictorRentea.ro Sensitive Specific Fast Few Clinical Tests 21 Professional Unit Testing – Principles of Test Design
- 21. VictorRentea.ro Sensitive High Coverage % Correct Tests Specific Expressive Isolated & Robust Low overlap Fast Few Small, DRY tests Test Design Goals 22 Professional Unit Testing – Principles of Test Design = Maintainable fail for any bug precise failures
- 22. VictorRentea.ro Test code >> Prod code Not maintainable? Under pressure, devs might: 23 Professional Unit Testing – Principles of Test Design @Ignore delete test delete asserts // comment test invert asserts // @Test
- 24. VictorRentea.ro ▪Code that you fear 😱 (hard to understand) ▪A distant corner in the logic (takes 3 mins of UI clicks to reproduce) ▪A bug (before fixing it) 🏆 ▪for/if/while ⚙ ▪Thrown exception ▪A method that just calls two others ▪Trivial code ▪Legacy code with 0 bugs, 0 changes (over the last year) Testing Priorities 25 Professional Unit Testing – Basics PRIORITY a.setName(b.getName()); *in case you're not 100% TDD
- 25. VictorRentea.ro Tests are green. You implement a huge CR in Prod code. Tests are green. Evergreen Tests 26 We ❤ Green Tests!
- 29. VictorRentea.ro30 How can you check that your test really covers what it says?
- 30. VictorRentea.ro33 Professional Unit Testing – Test Design Guidelines Mutation Testing You make some change to the Production code You get some "mutant" code The tests should squash the mutant by turning red You run the Tests You undo the change There are frameworks that play like this with your code, but their results might be depressing Tests fail ֞ Production code is altered How can you check that your test really covers what it says?
- 31. VictorRentea.ro Always see your test failing at least once 34 Tests, like laws, are meant to be broken
- 32. VictorRentea.ro ▪Regression - Yeehaaa! ➔ fix it ▪Change Request - Double Check ➔ Update/Delete it ? ▪Iso-functional changes - Superficial API Changes ➔ adjust the test - Refactoring internals ➔ loosen the test coupling ▪A Bug in a Test - Usually discovered via debugging ➔ fix the test Why can a Test Fail ? 35 Professional Unit Testing – Test Design Guidelines the usual suspect = production code
- 33. VictorRentea.ro A Bug in a Test 36 Professional Unit Testing – Test Design Guidelines
- 34. VictorRentea.ro37 Professional Unit Testing – Test Design Guidelines A Bug in a Test
- 35. VictorRentea.ro38 Professional Unit Testing – Test Design Guidelines
- 36. VictorRentea.ro39 Professional Unit Testing – Test Design Guidelines
- 37. VictorRentea.ro Concatenation, arithmetic 40 Professional Unit Testing – Test Design Guidelines assertEquals("Greetings" + name, logic.getGreetings(name)); if, switch Did you also tested that logic? ("test the tests" ☺) it's missing a " "! Why? The same Dev wrote both prod and test code! ☺ CPP ➔ Prefer literals assertEquals("Greetings John", logic.getGreetings("John")); Can you find the bug?
- 38. VictorRentea.ro catch-assert When you want to verify an exception is thrown 41 Professional Unit Testing – Test Design Guidelines try { logicThatShouldThrow(); fail("should have thrown"); } catch (MyException ex) { assert("msg", ex.getMessage()); } Can you find the bug?
- 39. VictorRentea.ro Verify an Exception Type is Thrown 42 Professional Unit Testing – Test Design Guidelines @Rule public ExpectedException exception = none(); @Test public void expectExceptionWithDetails() { exception.expectMessage("contains this"); // or… exception.expect(exceptionWithCode(FILE_LOCKED)); // throwing code } @Test(expected = IllegalArgumentException.class) public void expectExceptionTypeThrown() { // throwing code } Verify Exception Message/Code For precision: let's create 20 new Exception classes ! Hamcrest
- 40. VictorRentea.ro Junit 5 43 Professional Unit Testing – Test Design Guidelines @Test public void assertException() { IllegalArgumentException ex = assertThrows( IllegalArgumentException.class, () -> throwingProdCode()); assertEquals(FILE_LOCKED, ex.getErrorCode()); }
- 41. VictorRentea.ro for loop Testing a set of input-output pairs? ➔ Parameterized Unit Tests ➔ .feature files 46 Professional Unit Testing – Test Design Guidelines WHY?!
- 42. VictorRentea.roProfessional Unit Testing – Test Design Guidelines @RunWith(Parameterized.class) public class FizzBuzzTest { private final int number; private final String expected; public FizzBuzzTest(int number, String expected) { this.number = number; this.expected = expected; } @Parameters(name="For {0}, returns "{1}"") public static List<Object[]> getParameters() { return asList( new Object[] {1, "1"}, new Object[] {2, "2"}, new Object[] {5, "Buzz"}, new Object[] {3*5, "Fizz Buzz"}, new Object[] {3*7, "Fizz Wizz"}, [...] ); } @Test public void checkNumber() { assertEquals(expected, FizzBuzz.getNumber(number)); } } (instead of asserting in a loop) ParameterizedTests 47
- 43. VictorRentea.ro Can be signed directly by Biz guys ! .feature files 48
- 44. VictorRentea.ro multi-thread Looking for a race bug with sleep(random) ? ➔ Use-Your-Brain™ instead 51 Professional Unit Testing – Test Design Guidelines asserting time random Testing to find errors? ➔ replay real calls from production (Even more: Golden Master Technique)
- 45. VictorRentea.ro52 Professional Unit Testing – Test Design Guidelines dependencies TimeMachine.setTestClockAt(time); actual = callProd(…); assertEquals(new Date(), actual); assertEquals(time, actual); fails/passes randomly! return TimeMachine.now(); return new Date(); return LocalDateTime.now();+1ms? asserting time your custom class Let's truncate! :D draconian PowerMock?
- 46. VictorRentea.ro53 Professional Unit Testing – Test Design Guidelines Tests Can Control the Time
- 47. VictorRentea.ro databases 56 Professional Unit Testing – Test Design Guidelines files queues external web services These are Integration Tests
- 48. VictorRentea.ro GREEN ZONE Integration vs Unit Tests 57 Professional Unit Testing – Test Design Guidelines Deep Testing through many layers Fragile (DB, files, external systems) Their failure is not always a bug Super-Fast 100 tests/sec (some can be slower) Slow start-up the container In-mem DB
- 49. VictorRentea.ro Sensitive High Coverage % Correct Tests Specific Expressive Isolated & Robust Low overlap Fast Few Small, DRY tests Test Design Goals 60 Professional Unit Testing – Principles of Test Design
- 50. VictorRentea.ro Minimize Duplication 61 public void myTestRaw() { Order o = new Order(); o.setDate(new Date()); o.setLines(new ArrayList<OrderLine>()); OrderLine ol1 = new OrderLine(); ol1.setProduct("P1"); ol1.setItems(3); o.getLines().add(ol1); OrderLine ol2 = new OrderLine(); ol2.setProduct("P2"); ol2.setItems(null); o.getLines().add(ol2); target.process(o); } Data Initialization
- 51. VictorRentea.ro66 Professional Unit Testing – Test Design Guidelines public void myTestWithBuildersAndObjectMother() { Order o = anOrderWithOneLine() .with(anOrderLine().withItem(anItem())) .build(); target.process(o); } Fluent Builder Object Mother
- 52. VictorRentea.ro ▪Fluent Builder® ▪Factory methods - Object Mother shared between tests ? ▪Wrap production API - In a more testable API ▪Keep common stuff in fields ▪Shared @Before DRY Tests 67 Professional Unit Testing – Test Design Guidelines Safe Each @Test runs on a fresh instance of the Test class
- 53. VictorRentea.ro Sensitive High Coverage % Correct Tests Specific Expressive Isolated & Robust Low overlap Fast Few Small, DRY tests Test Design Goals 68 Professional Unit Testing – Principles of Test Design
- 54. VictorRentea.ro @Before You want to shrink a large test Abusing @Before ==Practical Guide☺== 69 Professional Unit Testing – Test Design Guidelines You move some code in the @Before ▪ Data initialization ▪ Mocks ▪ Infra setup: DB, .. Other tests do the same: And time passes by When you read a test: ▪ Arrange = method + @Before ▪ What part of it ?
- 55. VictorRentea.ro SingleTestClass ATest BTest Fixture-Based Test Breakdown 70 Professional Unit Testing – Test Design @Before Nested Test Fixtures in JUnit5: https://junit.org/junit5/docs/current/user-guide/#writing-tests-nested @Test @Test @Test sharedA @Test @Test @Test @Test @Test @Before @Test @Test @Test @Test @Test @Test @Test @Test @Before sharedB
- 56. VictorRentea.ro Start with one Test class/Prod class - If it grows (>300 lines?) or - If many tests share a fixture Split it 71 Professional Unit Testing – Test Design Guidelines RecordRepositoryTest RecordRepositorySearchForVersionTest Maybe also split the prod code ?
- 57. VictorRentea.ro 5-10 lines Descriptive names Test Methods 72 Professional Unit Testing – Test Design Guidelines public void givenAnInactiveCustomer_whenHePlacesAnOrder_itIsActivated() public void getRecordDeltasForVersionWithDeletedRecord() public void givenAProgramLinkedTo2Records_whenUpdated_2AuditsAreInserted( RecordRowValidatorTest.invalidRecordStartDateFormat()
- 58. VictorRentea.ro AnInactiveCustomerShould .beActivatedWhenHePlacesAnOrder() A Naming Convention 73 Professional Unit Testing – Test Design Guidelines "Given" = the class name ~ @Before No need for method prefixes Test names start with "Then" part the expectations "When" follows https://codurance.com/2014/12/13/naming-test-classes-and-methods/
- 60. VictorRentea.ro Suggestive Literals 75 Professional Unit Testing – Test Design Guidelines @Test public void customerEmailIsUpdated() { Long customerId = createCustomer(new Customer("oldPhone")); updateCustomerPhone(customerId, "newPhone"); Customer updatedCustomer = getCustomer(customerId); assertEquals("newPhone", updatedCustomer.getPhone()); }
- 61. VictorRentea.ro Assert a collection Beautiful Failure Messages (an example) 76 Professional Unit Testing – Test Design Guidelines assertEquals(1, names.size()); assertEquals("name", names.iterator().next()); assertEquals(Collections.singleton("name"), names); vs
- 62. VictorRentea.ro Try to name this test: ➔ Break it in 2 tests (perhaps break the Prod too? ~ CQS) Single Assert Rule one feature/test 77 Professional Unit Testing – Test Design Guidelines assertEquals("FN", customer.getFirstName()); assertEquals("LN", customer.getLastName()); assertEquals(Status.SUCCESS, result); verify(emailService).sendEmail(anyObject());
- 63. VictorRentea.ro Sensitive High Coverage % Correct Tests Specific Expressive Isolated & Robust Low overlap Fast Few Small, DRY tests Test Design Goals 78 Professional Unit Testing – Principles of Test Design
- 65. VictorRentea.ro Fresh code: Test through the public API Tests won't break when implem changes Practices the API Legacy code: Breaking encapsulation is a core technique Temporarily use package/public protection 80 Professional Unit Testing – Test Design Guidelines
- 66. VictorRentea.ro You run your test suite Test #13 is RED To debug it, you run it alone: Test #13 is GREEN ??!!!?! Yet Another Happy Day#2… 81 Professional Unit Testing – Testing on DB
- 67. VictorRentea.ro You run your test suite It's GREEN You add Test #43 Test #13 turns RED (unchanged!) You delete Test #43 Test #13 goes back GREEN Yet Another Happy Day#3… 82 Professional Unit Testing – Testing on DB ??!!!?!
- 68. VictorRentea.ro ▪In-memory Objects ▪COMMITs to DB ▪External files/systems Hidden Test Dependencies 83 Professional Unit Testing – Testing on DB - Static fields, singletons - PowerMocks - Thread Locals - Container shared by tests [Spring] - In-memory or external ➔ Reset them in @Before
- 69. VictorRentea.ro JUnit runs tests in unexpected order To Ensure Independency 84 Professional Unit Testing – Testing on DB (DON'T DO THIS) @FixMethodOrder(MethodSorters.NAME_ASCENDING)
- 70. VictorRentea.ro Sensitive High Coverage % Correct Tests Specific Expressive Isolated & Robust Low overlapping Fast Few Small, DRY tests Test Design Goals 86 Professional Unit Testing – Principles of Test Design
- 71. VictorRentea.ro ▪Test Design Principles ▪TDD ▪Mocks ▪Databases ▪Legacy Code Agenda 87
- 72. VictorRentea.ro A discipline in which you grow software in small increments for which you write the tests before the implementation TDD 88 Professional Unit Testing – TDD Credited to Kent Beck, 2003
- 73. VictorRentea.ro TDD Mantra Red-Green-Refactor 90 Professional Unit Testing – TDD With Grace fail KISS, YAGNI, Golf: Write as little prod code, don’t mind about quality You can't break anything •Start with the simplest cases •Start with the ☺ flows If you get stuck or other tests break => revert and retry DRY, Clean Code Write prod code to Make It PassWrite a Failing Test for a new feature Refactor prod + tests pass fail Run Tests Run Tests Run Tests 1-10 min Overlapping? – Incorrect? – Rules of Simple Design
- 74. VictorRentea.ro Rules of Simple Design 91 Professional Unit Testing – TDD - Kent Beck https://martinfowler.com/bliki/BeckDesignRules.html 2. Reveals Intention 3. No Duplication 4. Fewest Elements 1. Passes the Tests
- 75. VictorRentea.ro TDD Schools of Thought 92 Professional Unit Testing – TDD TDD as if you meant it
- 76. VictorRentea.ro ▪Test Design Principles ▪TDD ▪Mocks ▪Databases ▪Legacy Code Agenda 101
- 77. VictorRentea.ro Fake Objects 102 Professional Unit Testing – Mocking Fast DB ☺ Repeatable Isolation from external systems Mentally Simpler To test a layer, fake the layer bellow: WHY?!
- 79. VictorRentea.ro Fake 104 Professional Unit Testing – Mocking Mock Verify a method call verify(repo).save(…); Stub Respond to method calls when(mock.method()) .thenReturn(…); The confusion:
- 80. VictorRentea.ro The Circle of Purity 106 Professional Unit Testing – Mocking
- 81. VictorRentea.ro Side-effects 1)On external systems: 2)On in-memory objects ➔ assert their state What can a Unit Test check? 107 Professional Unit Testing – Mocking Input OutputFeature (prod function) Data from dependencies Input+Deps → Output (real or stubbed) a)Real: SELECT b)Mock: verify repo.save() was called Input → Output Simple and Elegant Pure function: 𝑓 𝑥 = 𝑥2 Simplify design: purify logic
- 82. VictorRentea.ro108 Professional Unit Testing – The Circle of Purity Extract Method mock stub
- 83. VictorRentea.ro109 Professional Unit Testing – The Circle of Purity = Pure Function
- 85. VictorRentea.ro Verify every method call How many times calls happen times(1) No extra call happen Capture-assert every argument 115 Professional Unit Testing – Mocking
- 87. VictorRentea.ro Object 119 query command inbound outbound to self What to test? Inspiredfrom:SandiMetz-Themagictricksoftestinghttps://www.youtube.com/watch?v=URSWYvyc42M
- 88. VictorRentea.ro query command inbound assert assert to self ignore ignore outbound ignore verify Minimalistic Testing 120 Inspiredfrom:SandiMetz-Themagictricksoftestinghttps://www.youtube.com/watch?v=URSWYvyc42M
- 89. VictorRentea.ro Which API is stable? Yet reachable? Where to Slice it? 121 A B C D nearest edge final real system intermediary TEST
- 90. VictorRentea.ro It may be simpler to test some classes together! 122 (versus testing them separately using mocks)
- 91. VictorRentea.ro127 Professional Unit Testing – Mocking OrderService EmailService PARTIAL MOCK (normal)MOCK private sendEmail() public sendEmail() Separation by Layers of Abstraction A Tale about the Evil Partial Mock... Refactor using mocks Which methods are more abstract ? (i.e. higher-level)Don’t do that !! Partial Mocks are Evil ! Oh!.. Why? Dunno.. @Autowired Tests overlap!! public placeOrder() public shipOrder() a.k.a. “spy”
- 92. VictorRentea.ro ▪Test Design Principles ▪TDD ▪Mocks ▪Databases ▪Legacy Code Agenda 141
- 93. VictorRentea.ro142 Professional Unit Testing – Recap First couple of unit tests: Priceless Test no. difficulty
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- 99. VictorRentea.ro ▪Extract-'n-test - Then mock it out ▪Break encapsulation - Expose internal state - Spy internal methods ▪Hack statics - PowerMock methods - Control global state ▪Introduce Seams - Decoupling places ▪Exploratory refactoring - 30 mins that you always throw away - Search for ways to break the design to become more testable ▪IDE Refactoring only - When not guarded by tests - Mob ▪Temporary ugly tests ▪Unit Test + Refactoring - Always together! Some Techniques for Testing Legacy Code 150 Professional Unit Testing – Legacy Code More on: http://blog.adrianbolboaca.ro/2015/02/unit-testing-on-legacy-code/
- 100. VictorRentea.ro151
- 101. VictorRentea.ro Testing Legacy Code: Feeling 153 Professional Unit Testing – Recap https://www.youtube.com/watch?v=_gQ84-vWNGU
- 102. VictorRentea.ro Testing Legacy Code Golden Master Technique 154 Professional Unit Testing – Recap http://blog.adrianbolboaca.ro/2014/05/golden-master/ original refactored same input same output same interactions Idea: record these in production, then replay them on your refactor
- 103. VictorRentea.ro ▪ Clean Code + Clean Coders Videos [CCEp#] http://www.cleancoders.com/ Robert C. Martin (Uncle Bob) ▪ (London-Style TDD): Growing Object-Oriented Software, Guided by Tests Steve Freeman, Nat Pryce, 2009 ▪ (Classic-Style TDD): Test-Driven Development, by example Kent Beck, 2000 ▪ The Art of Unit Testing Roy Osherove, 2009 ▪ Coding Dojo Handbook Emily Bache, 2009 ▪ https://springtestdbunit.github.io/spring-test-dbunit/faq.html ▪ Professional TDD with C#: Developing Real World Apps with TDD James Bender, Jeff McWherter, 2011 ▪ Agile in a Flash: https://pragprog.com/book/olag/agile-in-a-flash ▪ "Is TDD Dead?" - on You Tube ▪ Introducing BDD: http://dannorth.net/introducing-bdd/ Dan North ▪ Refactoring Martin Fowler, 1999 References 156 Professional Unit Testing – Further Reading
- 104. VictorRentea.ro ▪Test where the Fear is ▪Correct Tests fail Prod mutates ▪Explicit, Simple Tests ▪TODO: Try TDD! ▪Purify the heavy logic ▪Listen to Tests: Testable Design Key Points 157
- 105. VictorRentea.ro158 End of Part 1 Trainings, talks, goodies Daily posts on Let's chat! What do you want after the break? Proxies; Legacy Kata; TDD; Java8 Vote here: victorrentea.ro/vote Come take 1 sticker: