Junit Training

Chris Yeung 8

th

Sept, 2006

Introduction

• JUnit is a regression testing framework • Written by Erich Gamma and Kent Beck.

• Used by developers to implement unit tests in Java • Goal: Accelerate programming and increase the quality of code.

• Part of XUnit family (HTTPUnit, Cactus), CppUnit

Why test? Why Junit?

• Automated tests prove features • Tests retain their value over time and allows others to prove the software still works (as tested). • Confidence, quality, sleep • Effective, open source, integrated • Get to code sooner by writing tests.

What is Junit?

• Test framework provides tools for: – assertions – running tests – aggregating tests (suites) – reporting results • Philosophy always the same: – Let developers write tests.

– Make it easy and painless.

– Test early and test often

Test infected

• It’s a Good Thing, no penicillin needed • Immediate gratification with build iterations – Start with “The Simplest Thing That Could Possibly Work”.

– Iterate by successive application of design pattern.

• Break the cycle of more pressure == fewer tests • Reduce code captivity – If others can test it, others can work on it.

Junit Mechanics

• Define a subclass of

TestCase.

• Override the

setUp() & tearDown()

methods.

• Define one or more public

testXXX()

methods – Exercise the object(s) under test.

– Asserts the expected results.

• Define a static

suite()

factory method – Create a TestSuite containing all the tests.

• Optionally define batch mode .

main()

to run the TestCase in

Junit Mechanics

Simple Testcase

public class StringTest extends TestCase { protected void setUp(){ /* run before */} protected void tearDown(){ /* after */ } } public void testSimpleAdd() { String s1 = new String(“abcd”); String s2 = new String(“abcd”); assertTrue(“Strings not equal”, s1.equals(s2)); } public static void main(String[] args){ } junit.textui.TestRunner.run (suite ());

Simple Testcase (cont.)

public static Test suite (){ suite = new TestSuite (”StringTest"); String tests = System.getProperty("tests"); if (tests == null){ suite.addTest(new TestSuite(StringTest.class)); }else{ StringTokenizer tokens = new StringTokenizer(tests, ","); while (tokens.hasMoreTokens()){ suite.addTest(new StringTest((String)tokens.nextToken())); } } return suite; }

• • •

Other assertion methods

assertEquals(

expected

,

actual

) assertEquals(String

message

,

expected

,

actual

) – This method is heavily overloaded: arg1 both objects or and arg2 both of the same primitive type must be – For objects, uses your equals method,

if

you have defined it properly, as public boolean equals(Object o) --otherwise it uses == assertSame(Object assertSame(String

expected

, Object

message

, Object Object

actual

)

actual

)

expected

, – Asserts that two objects refer to the same object (using == ) assertNotSame(Object assertNotSame(String

expected

, Object

message

, Object Object

actual

)

actual

)

expected

, – Asserts that two objects do not refer to the same object

Other assertion methods

• assertNull(Object assertNull(String

object

)

message

, Object – Asserts that the object is null

object

) • assertNotNull(Object assertNotNull(String

object

)

message

, Object – Asserts that the object is null

object

) • fail() fail(String

message

) – Causes the test to fail and throw an AssertionFailedError – Useful as a result of a complex test, when the other assert methods aren’t quite what you want

What should I test?

• Tests things which could break • Tests should succeed quietly.

– Don’t print “Doing foo…done with foo!” – Negative tests, exceptions and errors • What shouldn’t I test – Don’t test set/get methods – Don’t test the compiler

Fixtures

• Handle common objects under test • setup() and tearDown() used to initialize and release common objects.

• Used to insure there are no side effects between tests.

• Enforce the test independence rule, test execution order is not guarunteed.

Execrise

• Write a testcase to test 3 method of java.util.ArrayList

Test Suites

public static void main (String [] args){ junit.textui.TestRunner.run (suite ()); } public static Test suite (){ suite = new TestSuite ("AllTests"); suite.addTest (new TestSuite (AllTests.class)); suite.addTest (StringTest.suite()); public void testAllTests () throws Exception{ assertTrue (suite != null); } }

TestRunners

• Text – Lightweight, quick quiet – Run from command line

java StringTest ....... Time: 0.05

Tests run: 7, Failures: 0, Errors: 0

TestRunners - Swing

• Run with java junit.swingui.TestRunner

Test Runners - Eclipse

Automating testing (Ant)

• Junit Task

Ant Batch mode

Designing for testing

– Separation of interface and implementation • Allows substitution of implementation to tests – Factory pattern • Provides for abstraction of creation of implementations from the tests. – Strategy pattern • Because FactoryFinder dynamically resolves desired factory, implementations are plugable

Design for testing - Factories

•

new

only used in Factory • Allows writing tests which can be used across multiple implementations.

• Promotes frequent testing by writing tests which work against objects without requiring extensive setup – “extra-container” testing.

Design for testing - Mock Objects

• When your implementation requires a resource which is unavailable for testing • External system or database is simulated.

• Another use of Factory, the mock implementation stubs out and returns the anticipated results from a request.

Example of using Mock Object

import org.jmock.*; class PublisherTest extends MockObjectTestCase { public void testOneSubscriberReceivesAMessage() { // set up, subscriber can be any class Mock mockSubscriber = mock(Subscriber.class); Publisher publisher = new Publisher(); publisher.add((Subscriber) mockSubscriber.proxy()); final String message = "message"; // expectations mockSubscriber.expects(once()).method("receive").with( eq(message) ); // execute publisher.publish(message); } } • Of course, you can write mock yourself by implement interface with simple implementation

Testing with resources (EJB/DB)

• Use fixtures to request resource connection via factory, could be no-op.

• Use vm args or resource bundle to drive which factory is used.

• Data initialization/clearing handled by fixtures to preserve order independence of tests.

}

Develop testcase with database using abstract base class

public abstract class DatabaseTestCase extends TestCase } } } } } resetData(); DefaultDataManager.setupDefaultData(); databaseSetUp(); this.databaseTearDown(); this.getConnection().close(); public final Connection getConnection() { return currentContext.connection; { protected final void setUp() throws SQLException, IOException { protected final void tearDown() throws SQLException { protected void databaseSetUp() throws SQLException, IOException { protected void databaseTearDown() throws SQLException {

In-container unit testing

• There are tools like cactus and StrutsTestCase • Excellent for testing: – EJB – Servlets, Filters, Taglibs – Container-dependent frameworks, like Struts

JUnit Best Practices

• • • • • Separate production and test code But typically in the same packages Compile into separate trees, allowing deployment without tests Don’t forget OO techniques, base classing 1.

2.

3.

4.

5.

Test-driven development Write failing test first Testing for Exceptions Test then Fix Test then Refactor Where should I put my test files?

Write failing test first

• Write your test first, or at least at the same time • Test what can break • Create new tests to show bugs then fix the bug • Test driven development says write the test then make it pass by coding to it.

Testing for Exceptions

public void testExpectException() { String s1 = null; String s2 = new String("abcd"); try{ s1.toString(); fail("Should see null pointer"); } catch(NullPointerException ex){ } }

Test then Fix

• Bugs occasionally slip through (gasp!) • Write a test first which demonstrates the error. Obviously, this test is needed.

• Now, fix the bug and watch the bar go green!

• Your tests assure the bug won’t reappear.

Test then Refactor

• Once the code is written you want to improve it.

• Changes for performance, maintainability, readability.

• Tests help you make sure you don’t break it while improving it.

• Small change, test, small change, test...

Where should I put my test files?

You can place your tests in the same package and directory as the classes under test. For example:

src com xyz SomeClass.java

SomeClassTest.java

An arguably better way is to place the tests in a separate parallel directory structure with package alignment. For example:

src com xyz SomeClass.java

test com xyz SomeClassTest.java

These approaches allow the tests to access to all the public and package visible methods of the classes under test.

Resources

• http://www.junit.org

• http://www.xprogramming.com

• http://www 106.ibm.com/developerworks/java/library /j-junitmail/index.html

• http://jakarta.apache.org/ant