The document provides an overview of test-driven development (TDD) principles and practices for keeping normal blood pressure. It discusses what TDD is, basic TDD principles like "tests first" and writing minimal code to pass tests, benefits like better design and refactoring, and challenges like requiring discipline. It provides examples of writing tests for a FizzBuzz game in a test-first manner, demonstrating how to name tests clearly and structure them. It also discusses tools like Mockito for mocking and Cobertura for checking code coverage targets.

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