JUnit 4

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JUnit 4
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Comparing JUnit 3 to JUnit 4

• All the old assertXXX methods are the same
• Most things are about equally easy
• JUnit 4 makes it easier to test that exceptions
  are thrown when they should be
• JUnit 4 can still run JUnit 3 tests
• JUnit 4 provides protection against infinite
  loops
• JUnit 4 has some additional features

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Migrating from JUnit 3

• JUnit 4 requires Java 5 or newer
• Dont extend junit.framework.TestCase just use
  an ordinary class
• Import org.junit. and org.junit.Assert.
• Use a static import for org.junit.Assert.
• Static imports replace inheritance from
  junit.framework.TestCase
• Use annotations instead of special method names
• Instead of a setUp method, put _at_Before before
  some method
• Instead of a tearDown method, put _at_After before
  some method
• Instead of beginning test method names with
  test, put _at_Test before each test method

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Writing a JUnit test class, I

• Start by importing the JUnit 4 classes you need
• import org.junit.import static
  org.junit.Assert.
• Declare your class in the usual way
• public class MyProgramTest
• Declare any variables you are going to use
  frequently, typically including an instance of
  the class being tested
• MyProgram programint arrayint solution

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Writing a JUnit test class, II

• If you wish, you can declare one method to be
  executed just once, when the class is first
  loaded
• This is for expensive setup, such as connecting
  to a database
• _at_BeforeClasspublic static void setUpClass()
  throws Exception // one-time
  initialization code
• If you wish, you can declare one method to be
  executed just once, to do cleanup after all the
  tests have been completed
• _at_AfterClasspublic static void tearDownClass()
  throws Exception // one-time cleanup
  code

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Writing a JUnit test class, III

• You can define one or more methods to be executed
  before each test typically such methods
  initialize values, so that each test starts with
  a fresh set
• _at_Beforepublic void setUp() program new
  MyProgram() array new int 1, 2, 3, 4,
  5
• You can define one or more methods to be executed
  after each test typically such methods release
  resources, such as files
• _at_Afterpublic void tearDown()

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_at_Before and _at_After methods

• You can have as many _at_Before and _at_After methods
  as you want
• Be warned You dont know in what order they will
  execute
• You can inherit _at_Before and _at_After methods from a
  superclass execution is as follows
• Execute the _at_Before methods in the superclass
• Execute the _at_Before methods in this class
• Execute a _at_Test method in this class
• Execute the _at_After methods in this class
• Execute the _at_After methods in the superclass

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Writing a JUnit test class, IV

• A test method is annotated with _at_Test, takes no
  parameters, and returns no result
• All the usual assertXXX methods can be used
• _at_Testpublic void sum() assertEquals(15,
  program.sum(array)) assertTrue(program.min(ar
  ray) gt 0)

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Special features of _at_Test

• You can limit how long a method is allowed to
  take
• This is good protection against infinite loops
• The time limit is specified in milliseconds
• The test fails if the method takes too long
• _at_Test (timeout10) public void greatBig()
  assertTrue(program.ackerman(5, 5) gt 10e12)
• Some method calls should throw an exception
• You can specify that a particular exception is
  expected
• The test will pass if the expected exception is
  thrown, and fail otherwise
• _at_Test (expectedIllegalArgumentException.class)pu
  blic void factorial() program.factorial(-5)
  

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Parameterized tests

• Using _at_RunWith(valueParameterized.class) and a
  _at_Parameters method, you can run the same tests
  with multiple datasets
• _at_RunWith(valueParameterized.class)public class
  FactorialTest private long expected
  private int value _at_Parameters public
  static Collection data() return
  Arrays.asList( new Object 1, 0 , 1,
  1 , 2, 2 , 120, 5 ) public
  FactorialTest(long expected, int value) //
  constructor this.expected expected
  this.value value _at_Test
  public void factorial()
  assertEquals(expected, new Calculator().factorial(
  value))
• Source http//today.java.net/pub/a/today/2006/12/
  07/junit-reloaded.html

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Ignoring a test

• The _at_Ignore annotation says to not run a test
• _at_Ignore("I dont want Dave to know this doesnt
  work")_at_Testpublic void add()
  assertEquals(4, program.sum(2, 2))
• You shouldnt use _at_Ignore without a very good
  reason!

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Test suites

• As before, you can define a suite of tests
• _at_RunWith(valueSuite.class)_at_SuiteClasses(valueM
  yProgramTest.class,
  AnotherTest.class)public class AllTests

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Other stuff

• Failed tests now throw an AssertionError, rather
  than JUnit 3s AssertionFailedError
• There is now a version of assertEquals for arrays
  of objectsassertEquals(Object expected,
  Object actual)
• Unfortunately, there is still no assertEquals for
  arrays of primitives
• JUnit 3 had an assertEquals(p, p) method for each
  kind of primitive p, but JUnit 4 only has an
  assertEquals(object, object) and depends on
  autoboxing

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A gotcha

• The following method
• long sum(long x, long y) return x y
• with the following test
• _at_Testpublic void sum() assertEquals(4,
  s.sum(2, 2))
• gives
• expected lt4gt but was lt4gt
• This is due to your friend, autoboxing
• assertEquals no longer exists for primitives,
  only for objects
• Hence, the 4 is autoboxed to an Integer, while
  sum returns a long
• The error message means expected int 4, but got
  long 4
• To make this work, change the 4 to a 4L

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JUnit 4 in Eclipse and NetBeans

• As usual, the easiest way to create a test class
  is just to let your IDE do it for you
• Here is the recommended test-driven approach
• Create a class containing all the stub methods
  you initially think you will need
• Have the IDE create the test class, with all the
  test methods
• Repeat
• Write a test
• Make sure the test fails
• Write the method being tested
• Make sure the test now succeeds
• Note When you create the test class, NetBeans in
  particular puts a lot of garbage lines into each
  test method you can just delete these and put in
  your own code

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The End