Unit testing Java programs Using JUnit 3

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Unit testing Java programs Using JUnit 3

• 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

• How to write a test case
• Extends TestCase
• class MyTest extends TestCase
• A test method must have the signature
• public void testXxx() throws ExceptionsAsYouLike
• Generally you would like one test case pr. Java
  class
• The unit to test is a class.

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Fixtures setUp and tearDown

• Sometimes you have 2 or more tests that must run
  on the same data. To ease this JUnit introduces
  the concept of a fixture.
• 2 methods inherited from TestCase meant to be
  overridden
• setUp()
• Executed before each individual test
• tearDown()
• Executed after each individual test

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Test suites

• You get a lot of test cases (1 pr. Java class).
• To several test cases at once you define a test
  suite
• Make an object of class TestSuite
• Add the individual test cases to the TestSuite
• Run the TestSuite

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How to test exceptions

• Testing an expected exception
• try
• method()
• fail(Exception expected)
• catch (ExpectedException ex) / ignore /
• A test method must have the signature
• public void testXxx() throws Exception
• That means that you can throw any exception from
  a test method.
• However, if a test methods throws an exception it
  means that the test has not passed.

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NetBeans assistance

• NetBeans can assist you in making TestCases for
  individual Java class and in assembling the test
  cases into test suites.
• TestCase
• Tools ? JUnit tests
• JUnit generates empty (in fact failing) tests for
  each public / protected method in a Java class.
• Fill you the empty tests and run the test.
• Test suites
• New ? Test Suite
• JUnit generates a test suite of all the test
  cases in the current test package.

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Running tests

• JUnit test can be run in several ways
• With a graphical user interface
• junit.swingui.TestRunner
• Uses Swing classes for the GUI
• With a textual user interface
• Junit.textui.TextRunner
• NetBeans uses a textual user interface when you
  run a test case or suite.

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The internal structure of JUnit

• JUnit uses the Reflection API
• Objects of class Class are submitted to the test
  suites.
• From an object Class JUnit finds all methods
  named testXxx() and executes those methods.
• Calling setUp() before testXxx()
• And calling tearDown() after testXxx()

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Composite design pattern in JUnit

• JUnit uses the composite design pattern to
  organize individual test cases and test suites

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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