Unit testing Java programs Using JUnit 4

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Unit testing Java programs Using JUnit 4

• If it isn't tested, it doesnt work

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Requirements for tests

• Tests must be executable
• A test must clearly show whether it executed
  successfully or not
• The not-so-successful part of the test must not
  be buried in a pile of test reports.

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Which methods should be tested

• Test a method if you are not 100 sure that the
  method is correct.
• Methods that usually does not need testing
• Simple get and set methods
• However, you might call get and set methods in
  testing other (more complex) methods
• Simple toString methods

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Individual test cases

• Annotate the test method with _at_org.junit.Test
• No need to extends any classes or use special
  method names
• Unlike JUnit 3
• Generally you would like one test class pr. Java
  class
• The unit to test is a class.

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Fixtures Before and After

• Sometimes you have 2 or more tests that must run
  on the same data.
• To ease this JUnit introduces the concept of a
  fixture.
• You can annotate 2 methods in your test class
  from
• _at_org.junit.Before
• Executed before each individual test
• Used to initialize test data
• Used quite often
• _at_org.junit.After
• Executed after each individual test
• Used to clean up after the test
• Examples Close database or socket connections
• Not used very often

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How to test exceptions

• JUnit 3 Testing an expected exception
• try
• method()
• fail(Exception expected)
• catch (ExpectedException ex) / ignore /
• JUnit 4 Testing an expected exception
• Use an annotation
• _at_Test (expected SomeException.class) public
  void testMetod()
• If testMethod() does not throw SomeException the
  test fails.

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NetBeans assistance

• JUnit is a plugin to NetBeans
• And many other IDEs
• NetBeans can assist you in making TestCases for
  individual Java class and in assembling the test
  cases into test suites.
• Right click the class you want to test
• Tools ? JUnit tests
• Choose JUnit 4 (not JUnit 3)
• JUnit generates empty tests for each public /
  protected method in a Java class.
• Fill you the empty tests and run the test.
• Like you run an ordinary program

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Testing in XP

• Testing is an important discipline in XP (Extreme
  Programming)
• XP idea Create the test before the code to be
  tested
• Writing the test makes you thing about detailed
  design
• Test is an executable requirements
• Writing (and running) test will be a positive
  experience.
• We know when a class is done
• When all tests run

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References

• Beck Gamma JUnit Cookbook,
• http//junit.sourceforge.net/doc/cookbook/cookboo
  k.htm
• Kent Beck Erich Gamma invented JUnit
• Martin Fowler Refactoring, Addison Wesley 2000
• Chapter 4 Building Tests, page 89-102
• Extreme Programming, Code the Unit Test First
  http//www.extremeprogramming.org/rules/testfirst.
  html
• Testing is an important discipline in XP (eXtreme
  Programming), which is another Kent Bech
  invention.
• Alex Garrett JUnit antipatterns
• http//www-128.ibm.com/developerworks/opensource/l
  ibrary/os-junit