28.01.2017? Speakers' Corner in Ciklum Dnipro

1. How to keep normal blood
pressure using TDD

2. A little bit about me
● Java developer at PrivatBank
● more than 3 years of experience
● much less experience in TDD
● blog: kastordriver.one
● e-mail: KastorDriver@gmail.com

3. Agenda
● what is TDD?
● basic principles of technique
● how to write tests correctly
● tools from the arsenal of Java developer
● some code and examples

4. Pyramid of fate tests
Unit tests
Integration tests
Manual
tests

5. What is TDD?
● tests first
● it is not about testing
● it is about design
● and little about documentation
● but they do not replace architecture and
design

6. Pros
● better design, because you think before writing
● documentation that we can trust
● fast feedback (faster than QA and debug)
● refactoring is encouraged
● minimalistic code

7. Cons
● not suitable for GUI and database schema development
● discipline is required
● discipline is required for all team members
● erroneous test leads to the erroneous code (problem?)

8. Test firstTest last

9. Test last
● we concentrate on the parts of the code instead of design
● by the time of writing tests we get tired
● tests are being wrote taking into account rakes and crutches
● “test last” requires a powerful self-organization (only superhero
is able to do that)

10. Test first
● write tests on the first wave of enthusiasm
● incentive for write code - pass the test
● look at issue from the user's perspective
● the code is tested and is minimal

11. Three laws of TDD
● You must not write code while tests
are red
● You must not be farther than one
step from green line
● You must not write code more than
necessary for passing tests

12. How does it look?
● think before writing test
● formalize business requirements in tests
● name of test has to clearly describe the
purpose of the test
● check that the test fails
Note: Tests clarity should be more important than avoiding code duplication
RED
GREENREFACTOR

13. How does it look?
● write enough code to compile and pass
the test. No more
● check that the test is passed
● check all other tests
RED
REFACTOR GREEN

14. How does it look?
● get rid of duplication
● think about design
● go to “red” step
GREENREFACTOR
RED

15. Provide correct tests names
You should not:
● name test same as tested method
● name tests like: testSomeMethod1, testSomeMethod2...

16. Provide correct tests names
Name of test should:
● describe feature or specification
● describe purpose of test
● describe what object does, but not what it is
● When [Action] Then [Verification]

18. @Test
public void whenNumberIsNotMultipleOf3And5ThenReturnTheSameNumber() {
FizzBuzzGame fizzBuzz = new FizzBuzzGame();
assertEquals(“1”, fizzBuzz.fizzBuzzNumber(1));
}

19. public class FizzBuzzGame {
public String fizzBuzzNumber(int number) {
return String.valueOf(1);
}
}

20. @Test
public void whenNumberIsNotMultipleOf3And5ThenReturnTheSameNumber() {
FizzBuzzGame fizzBuzz = new FizzBuzzGame();
assertEquals(“1”, fizzBuzz.fizzBuzzNumber(1));
assertEquals(“2”, fizzBuzz.fizzBuzzNumber(2));
}

21. public class FizzBuzzGame {
public String fizzBuzzNumber(int number) {
return String.valueOf(number);
}
}

22. private FizzBuzzGame fizzBuzzGame;
@Before
public void setUp() throws Exception {
fizzBuzzGame = new FizzBuzzGame();
}
@Test
public void whenNumberIsNotMultipleOf3And5ThenReturnTheSameNumber() {
assertEquals("1", fizzBuzzGame.fizzBuzzNumber(1));
assertEquals("2", fizzBuzzGame.fizzBuzzNumber(2));
}
@Test
public void whenNumberIsMultipleOf3ThenReturnFizz() {
assertEquals("Fizz", fizzBuzzGame.fizzBuzzNumber(3));
assertEquals("Fizz", fizzBuzzGame.fizzBuzzNumber(9));
}

23. public class FizzBuzzGame {
public String fizzBuzzNumber(int number) {
if (number % 3 == 0) return "Fizz";
return String.valueOf(number);
}
}

24. private FizzBuzzGame fizzBuzzGame;
@Before
public void setUp() throws Exception {
fizzBuzzGame = new FizzBuzzGame();
}
@Test
public void whenNumberIsNotMultipleOf3And5ThenReturnTheSameNumber() {
assertEquals("1", fizzBuzzGame.fizzBuzzNumber(1));
assertEquals("2", fizzBuzzGame.fizzBuzzNumber(2));
}
@Test
public void whenNumberIsMultipleOf3ThenReturnFizz() {
assertEquals("Fizz", fizzBuzzGame.fizzBuzzNumber(3));
assertEquals("Fizz", fizzBuzzGame.fizzBuzzNumber(9));
}
@Test
public void whenNumberIsMultipleOf5ThenReturnBuzz() {
assertEquals("Buzz", fizzBuzzGame.fizzBuzzNumber(5));
assertEquals("Buzz", fizzBuzzGame.fizzBuzzNumber(10));
}

25. public class FizzBuzzGame {
public String fizzBuzzNumber(int number) {
if (number % 3 == 0) return "Fizz";
if (number % 5 == 0) return "Buzz";
return String.valueOf(number);
}
}

26. private FizzBuzzGame fizzBuzzGame;
@Before
public void setUp() throws Exception {
fizzBuzzGame = new FizzBuzzGame();
}
@Test
public void whenNumberIsNotMultipleOf3And5ThenReturnTheSameNumber() {
assertEquals("1", fizzBuzzGame.fizzBuzzNumber(1));
assertEquals("2", fizzBuzzGame.fizzBuzzNumber(2));
}
@Test
public void whenNumberIsMultipleOf3ThenReturnFizz() {
assertEquals("Fizz", fizzBuzzGame.fizzBuzzNumber(3));
assertEquals("Fizz", fizzBuzzGame.fizzBuzzNumber(9));
}
@Test
public void whenNumberIsMultipleOf5ThenReturnBazz() {
assertEquals("Bazz", fizzBuzzGame.fizzBuzzNumber(5));
assertEquals("Bazz", fizzBuzzGame.fizzBuzzNumber(10));
}
@Test
public void whenNumberIsMultipleOf3And5ThenReturnFizzBazz() {
assertEquals("FizzBazz", fizzBuzzGame.fizzBuzzNumber(15));
assertEquals("FizzBazz", fizzBuzzGame.fizzBuzzNumber(30));
}

27. public class FizzBuzzGame {
public String fizzBuzzNumber(int number) {
if (number % 3 == 0) return "Fizz";
if (number % 5 == 0) return "Bazz";
if (number % 3 == 0 && number % 5 == 0) return "FizzBazz";
return String.valueOf(number);
}
}

28. public class FizzBuzzGame {
public String fizzBuzzNumber(int number) {
if (number % 3 == 0) return "Fizz";
if (number % 5 == 0) return "Bazz";
if (number % 3 == 0 && number % 5 == 0) return "FizzBazz";
return String.valueOf(number);
}
}
org.junit.ComparisonFailure:
Expected :FizzBazz
Actual :Fizz
. . .
FizzBuzzTest.whenNumberIsMultipleOf3And5ThenReturnFizzBazz(FizzBuzzTest.java:36)

29. public class FizzBuzzGame {
public String fizzBuzzNumber(int number) {
if (number % 3 == 0 && number % 5 == 0) return "FizzBazz";
if (number % 3 == 0) return "Fizz";
if (number % 5 == 0) return "Bazz";
return String.valueOf(number);
}
}

30. private FizzBuzzGame fizzBuzzGame;
@Before
public void setUp() throws Exception {
fizzBuzzGame = new FizzBuzzGame();
}
@Test
public void whenNumberIsNotMultipleOf3And5ThenReturnTheSameNumber() {
assertEquals("1", fizzBuzzGame.fizzBuzzNumber(1));
assertEquals("2", fizzBuzzGame.fizzBuzzNumber(2));
}
@Test
public void whenNumberIsMultipleOnlyOf3ThenReturnFizz() {
assertEquals("Fizz", fizzBuzzGame.fizzBuzzNumber(3));
assertEquals("Fizz", fizzBuzzGame.fizzBuzzNumber(9));
}
@Test
public void whenNumberIsMultipleOnlyOf5ThenReturnBazz() {
assertEquals("Bazz", fizzBuzzGame.fizzBuzzNumber(5));
assertEquals("Bazz", fizzBuzzGame.fizzBuzzNumber(10));
}
@Test
public void whenNumberIsMultipleOf3And5ThenReturnFizzBazz() {
assertEquals("FizzBazz", fizzBuzzGame.fizzBuzzNumber(15));
assertEquals("FizzBazz", fizzBuzzGame.fizzBuzzNumber(30));
}

31. public class FizzBuzzGame {
public String fizzBuzzNumber(int number) {
StringBuilder result = new StringBuilder();
if (number % 3 == 0) {
result.append("Fizz");
}
if (number % 5 == 0) {
result.append("Bazz");
}
return result.length() == 0 ? String.valueOf(number)
: result.toString();
}
}

32. Separate and rule your tests
http://www.kastordriver.one/2017/02/separate-and-rule-your-tests.html

33. Unit tests
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.19</version>
<configuration>
<includes>
<include>**/*Test.java</include>
</includes>
</configuration>
</plugin>

34. Integration tests
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-failsafe-plugin</artifactId>
<version>2.19.1</version>
<configuration>
<includes>
<include>**/*IT.java</include>
</includes>
</configuration>
<executions>
<execution>
<goals>
<goal>integration-test</goal>
<goal>verify</goal>
</goals>
</execution>
</executions>
</plugin>

35. We don't have time to write unit tests
Should I write code in a single
class with hundreds methods
without other classes, design
patterns and so on? No? But I
do not have time for that!
http://www.yegor256.com/2015/07/16/fools-dont-write-unit-tests.html

36. Are You Still Debugging?
Unit testing is a technique that
completely replaces
debugging. If debugging is
required, the design is not
good enough.
http://www.yegor256.com/2016/02/09/are-you-still-debugging.html

37. Legacy code

38. Legacy code
● write tests for legacy code
● rename, extract method, extract
interface
● write tests again
● sorry, but no fun

39. ● Mockito makes mocking very easy
● It is extremely easy to read mock code
● Mockito works in any environment and has no
external dependencies
Sip of mockito

40. import static org.mockito.Mockito.*;
// mock creation
List mockedList = mock(List.class);
// using mock object - it does not throw any "unexpected interaction" exception
mockedList.add("one");
mockedList.add("one");
mockedList.clear();
// selective, explicit, highly readable verification
verify(mockedList, times(2)).add("one");
verify(mockedList).clear();
You can verify interactions

41. @Test(expected = RuntimeException.class)
public void test() throws Exception {
// you can mock concrete classes, not only interfaces
LinkedList mockedList = mock(LinkedList.class);
// stubbing appears before the actual execution
when(mockedList.get(0)).thenReturn("first");
when(mockedList.get(1)).thenThrow(new RuntimeException());
// the following prints "null" because get(999) was not stubbed
assertNull(mockedList.get(999));
assertEquals("first", mockedList.get(0));
//throw RuntimeException
mockedList.get(1);
}
You can stub method calls

42. Be careful with mocks
● Don't mock type you don't own!
● Don't mock everything, it's an anti-pattern
● Don't mock value objects

43. Mockito discourages
● Can I mock static methods?
○ No. Mockito prefers object orientation
and dependency injection over static,
procedural code that is hard to
understand and change.
● Can I mock private methods?
○ No. From the standpoint of testing...
private methods don't exist.

44. ● Supports Mockito-style mocking.
● Mocks constructors, static, private and final
methods.
Powermock

45. class FileUtils {
public static Set<String> readUniqueWords(String path) throws IOException {
String text = new String(Files.readAllBytes(Paths.get(path)), "UTF-8");
Set<String> words = new HashSet<>();
for (String word : text.split(" ")) {
words.add(word);
}
return words;
}
}

46. @RunWith(PowerMockRunner.class)
@PrepareForTest({Files.class, FileUtils.class})
public class FileUtilsTest {
@Test
public void readUniqueWordsMustReturnOnlyUniqueWords() throws Exception {
final String somePath = "somePath";
Path fakePath = Paths.get(somePath);
PowerMockito.mockStatic(Files.class);
when(Files.readAllBytes(fakePath)).thenReturn("One two two three".getBytes());
Set<String> result = FileUtils.readUniqueWords(somePath);
assertEquals(3, result.size());
assertTrue(result.contains("One"));
assertTrue(result.contains("two"));
assertTrue(result.contains("three"));
}
}

47. class Text {
private final String path;
Text(String src) {
this.path = src;
}
public String readText() throws IOException {
return new String(Files.readAllBytes(Paths.get(this.path)), "UTF-8");
}
}

48. public class UniqueWords {
private final String text;
UniqueWords(String txt) {
this.text = txt;
}
public Set<String> readUniqueWords() {
Set<String> words = new HashSet<>();
for (String word : this.text.split(" ")) {
words.add(word);
}
return words;
}
}

49. public class UniqueWordsTest {
@Test
public void readUniqueWordsMustReturnOnlyUniqueWords() throws Exception {
Set<String> result = new UniqueWords("One two two three")
.readUniqueWords();
assertEquals(3, result.size());
assertTrue(result.contains("One"));
assertTrue(result.contains("two"));
assertTrue(result.contains("three"));
}
}

50. Odd man out

51. Cobertura maven plugin allows you:
● Check the coverage percentages for unit
tests and integration tests
● fail the build if the targets are not met
Keep a code coverage on a radar
http://www.kastordriver.one/2017/02/keep-code-coverage-on-radar.html

52. Useful links
Kent Beck "Test Driven Development"
Андрей Солнцев “Пацан накодил - пацан протестил!
Mockito wiki
Николай Алименков "Сага о том, как Java-
разработчики должны тестировать свои
приложения"
Victor Farcic, Alex Garcia "Test-Driven Java Development"

53. Thank you for your attention