The document discusses testing Java code using test-driven development (TDD). It covers TDD basics like writing tests before code, unit testing individual functions, and automatically running tests frequently. It provides examples of how to structure unit tests with arrangements, actions, and assertions and use mocking to isolate dependencies. Guidelines are given for writing testable code and utilizing features of testing frameworks like parameterized tests, expected exceptions, and matchers.

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Testing your code
For Java developers
Anna Khasanova
Anna.Khasanova@exigenservices.com
20 July 2015

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Agenda
• Testing basics
• TDD approach
• Testing in action
• Best practices
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What is a test? Why do we need it?
• What is test?
• Why do we need testing?
• Automation
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Automatic testing
Write once run often:
• Write test once
• Run frequently:
• After each change
• Continuous integration
• No human input
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TDD THEORY
What is Test Driven Development?
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Test Driven Development
• Software development approach
• Test before code
• Test - code requirements
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Advantages
• Increase requirements quality
• Increase code quality
• No unnecessary code
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New change request?
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Test fails
Write
test
Run test
Test succeeds
Design
Write
code
Test
succeeds
Run test
Test fails
Whole story covered
Test
succeeds
Refactor
code
Run test
Test fails
All tests succeed

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Bugfix?
• Get bug report
• Turn it into a test
• Test should fail
• Fix bug
• Test should pass
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THE PRACTICE
How should I work?
How to write tests?
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What is Unit Test?
• Automated test for
• One business unit
• One business case
• Isolated
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Unit Test is
• Small
• Fast
• Self documented
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3 parts of Unit-test
unitTest() {
// set preconditions: “arrange”
// call tested method: “act”
// assert results are as expected: “assert”
}
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Unit-Test libraries
• xUnit – collective naming: dbUnit,
htmlUnit, qUnit, etc.
• Java: jUnit
• Java: TestNG
• Javascript: jasmine
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Example of TDD
Telephone field validator:
• Allowed characters:
• numbers: [0-9]
• minus, space: “-” , “ ”
• Length: 10 digits (ignore spaces and minuses)
• Leading and trailing spaces are allowed
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REAL LIFE
Mock all dependencies
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We have a problem!
• Method uses web service
• or some other class/function
• We don’t want to test it
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Mock
• Fake implementation
• We set what mock returns
• Useful for unit-testing
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Mock libraries
• Mockito
• EasyMock
• jMock
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Example
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PicturesService
+getSquarePictures()
Repository
+getAllPictures()

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Example
@Test
public void testGetSquarePicturesEmptyResult() {
PicturesService testedService = new PicturesService();
Repository repository = mock(Repository.class);
when(repository.getAllPictures())
.thenReturn(Collections.<Picture>emptyList());
testedService.setRepository(repository);
Set<Picture> result = testedService.getSquarePictures();
assertTrue(result.isEmpty());
}
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//create fake Repository, returning empty list of pictures

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How to verify external calls?
• What to do if:
• Tested method should call externals
• We need to ensure that it was called?
• Mocks scenario verification
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Example
@Test
public void testDeleteSquarePicturesEmptyResult() {
PicturesService testedService = new PicturesService();
Repository repository = mock(Repository.class);
Mockito.when(repository.getAllPictures())
.thenReturn(Collections.<Picture>emptyList());
testedService.setRepository(repository);
testedService.deleteSquarePictures();
verify(repository, never()).deletePictures(any());
}
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How to verify arguments?
• What to do if:
• Mocked method is called with parameters
• We need to test passed parameters?
• Argument Captor
• Matchers
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Example
@Test
public void testDeleteSquarePictures_captor() {
…
ArgumentCaptor<Iterable> captor =
ArgumentCaptor.forClass(Iterable.class);
verify(repository).deletePictures(captor.capture());
Iterable<Picture> result = captor.getValue();
…
}
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How to verify exceptional cases?
• What to do if:
• Tested method should throw exception in
some case
• We need to test this case?
• Expected exceptions
@Test(expected = IllegalArgumentException.class)
public void testFactorialNegative() {
Factorial.factorial(-2);
}
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How to verify exceptional cases?
• What to do if:
• We need to test time of execution?
• Timeout parameter
@Test(timeout = 1000)
public void infinity() {
while (true) ;
}
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OTHER USEFUL FEATURES
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Other features: matchers
Matchers
• when(…), verify(…)
• assertThat(…)
• See hamcrest library
• Write your own
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Other features: runners
Test runners
• @RunWith
• Spring: SpringJUnit4ClassRunner
• Parameterized
• Any other
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SUMMARY. GUIDELINES.
To sum this all up…
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Coverage
• Coverage: what needs to be covered
• Setters-getters
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Above all
1. Understand requirements
2. Commit your understanding
• Java docs
• Any other
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Unit test
• One test – one case
• Each use case – covered
• Unit test != trash
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Write testable code
• Statics are evil
• Extract interfaces
• One method must not do “everything”
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Use framework’s features
• Parameterized tests
• Expected exceptions, timeouts
• Mock objects scenarios
• Matchers
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Finally
• Automatic testing – difficult to start, but…
• Don’t give up!
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QUESTIONS?
Your turn
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