Unit testing Java programs 1

Unit testing Java programs Using JUnit 4

“If it isn't tested, it doesn’t 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 @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– @org.junit.Before

• Executed before each individual test• Used to initialize test data• Used quite often

– @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 exceptiontry { method(); fail(“Exception expected”);}catch (ExpectedException ex) { /* ignore */ }

• JUnit 4: Testing an expected exception– Use an annotation

• @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 IDE’s

• 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/cookbook.htm

Kent Beck & Erich Gamma invented JUnit

Kent Beck JUnit https://github.com/KentBeck/junit/wiki Martin Fowler Refactoring, Addison Wesley 2000

Chapter 4 Building Tests, page 89-102Extreme 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/library/os-junit