Unit testing 101


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Unit Testing presentation I did for my company

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Unit testing 101

  1. 1. Unit Testing 101 Intro to What, Why, How
  2. 2. Outline 1. What is unit testing? a. what are units? b. testing the future, TDD 2. Why do we unit test? a. advantages i. refactoring ii. maintainability 3. How do we unit test? a. Guidelines b. Assertions c. Isolations d. Mocks vs Stubs 4. Related Stuff
  3. 3. What is Unit Testing? Kent Beck introduced the term legacy code: code without tests
  4. 4. What is Unit Testing Unified Process Requirements --> Use Cases, Scenarios Scenarios -> Classes, relationships classes(or functions in FP) are the units! Classes -> Unit Tests
  5. 5. Why Unit Testing? To fail when there is no harm to do so the cost to fix a bug in different stages did you think about that in advance? To refactor code (you can still refactor without UT) To test after development Self documenting code (if you read them)
  6. 6. How to do? ● one test, one scenario ○ no conditional statements like ■ if, switch etc ○ also no loops if possible ■ if there are loops, tests must be broken into other tests ● one test, one assertion ● isolated test, not depending on each ○ need dependency, use injection, not arbitrary tests ● do not handle exceptions ○ you can assert that an exception will be thrown, though ● tests are not functions of time!
  7. 7. How to do? when to add tests: ● before new classes/stories ● before fixing new bugs ○ preparing the test scenario ○ filling the gap ● before introducing new features you can also write tests for the completed code
  8. 8. How to do Unit Test Pattern: AAA : Arrange - Act - Assert
  9. 9. An Example in JUnit @RunWith(SpringJUnit4ClassRunner.class) @ContextConfiguration( {"file:test/test- config.xml", "file:web/WEB-INF/application- security.xml", "file:test/test-dao.xml"} ) public class MobileUtilsTest { @Autowired private MobileUtils mobileUtils; @Autowired private BankDao bankDao;
  10. 10. An Example in JUnit @Test public void testGenerateOtp() throws Exception { Bank bank = bankDao.findByBin ("402940"); String otp = mobileUtils.generateOtp (bank); System.out.println(otp); Assert.assertNotNull(otp); }
  11. 11. An Example in JUnit @Test(expected = NullPointerException.class) public void testGenerateNullBankOtp() throws Exception{ try{ Bank bank = null; String otp = mobileUtils.generateOtp (bank); } catch (Exception e){ throw e; } }
  12. 12. How to do Assertions: ● use as many as possible different types of assertions ○ assertThat, assertEquals, assertSame, assertNotNull ○ junit's matchers ● assertion statements must be readable ○ self documenting tests ○ not assertEquals( result, false ) ○ please do assertEquals( result, expectedResult )
  13. 13. How to do? Isolation is important: ● database isolation ○ use a test db if possible ● web container isolation ○ use dependency injection if possible ■ otherwise it is kind of integration testing ● see spring integration testing ● dependency injection ○ provides class isolation ● web services (rest & SOAP) ○ use mocks or stubs ● properties (file and system)
  14. 14. How to do? Automate the tests (otherwise they are meaningless) use tools like ant, maven Better use Jenkins!
  15. 15. How to do? If isolation is important, use mocks and stubs ○ mocks ■ use them when you have dependencies that cannot be fulfilled by writing simple stubs ● for example, an interface containing many method declarations ○ stubs ■ use them when you call inner methods to test the unit, so you don't have to write inner mocks too
  16. 16. How to do? Mocks vs Stubs: mocks depend on behavior verification while stubs depend on state verification examples from Martin Fowler:
  17. 17. Stub example public interface MailService { public void send (Message msg); } public class MailServiceStub implements MailService { private List<Message> messages = new ArrayList<Message>(); public void send (Message msg) { messages.add(msg); } public int numberSent() { return messages.size(); } }
  18. 18. Stub Example class OrderStateTester... public void testOrderSendsMailIfUnfilled() { Order order = new Order(TALISKER, 51); MailServiceStub mailer = new MailServiceStub(); order.setMailer(mailer); order.fill(warehouse); assertEquals(1, mailer.numberSent()); }
  19. 19. Mock Example class OrderInteractionTester... public void testOrderSendsMailIfUnfilled() { Order order = new Order(TALISKER, 51); Mock warehouse = mock(Warehouse.class); Mock mailer = mock(MailService.class); order.setMailer((MailService) mailer.proxy()); mailer.expects(once()).method("send"); warehouse.expects(once()).method("hasInventory") .withAnyArguments() .will(returnValue(false)); order.fill((Warehouse) warehouse.proxy()); //verify warehouse.verify(); assertTrue(order.isFilled()); } }
  20. 20. Mocks vs Stubs it really is a decision for TDD in mocks, you go outside in, one story at a time usually start from UI in stubs, you go middle out, also one story, can begin from business objects if your code is complete, use real objects, whenever possible (better code coverage)
  21. 21. mockists vs classical a comparison for TDD classical tries to use the existing objects in test mockist tries to mock complicated stuff and dependencies
  22. 22. For Existing Projects begin add tests submit to vcs keep tests in a separate folder/module test both for success and failure test the important features first or just write tests at all end
  23. 23. Relatives, Friends Code coverage Strive for 100% For starters, each project must have 20% remember the 20/80 rule use tools like http://www.jetbrains.com/idea/features/code_coverage.html Test Driven Development basis for TDD, write unit tests first! can try if you are starting a new project
  24. 24. Thank you Questions? (other than why this presentation is in English)
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