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Unit Testing with JUnit. CS 3331 Fall 2009 Kent Beck and Eric Gamma. Test Infected: Programmers Love Writing Tests, Java Report , 3(7):37-50, 1998. Available from: http://junit.sourceforge.net/doc/testinfected/testing.htm. Unit Testing. Introduction Conventional approach

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Unit testing with junit

Unit Testing with JUnit

CS 3331

Fall 2009

Kent Beck and Eric Gamma. Test Infected: Programmers Love Writing Tests, Java Report, 3(7):37-50, 1998.

Available from: http://junit.sourceforge.net/doc/testinfected/testing.htm

Unit testing
Unit Testing

  • Introduction

  • Conventional approach

  • Unit testing with JUnit

  • More on JUnit

Testing in general
Testing in General

  • Testing

    • A way of showing the correctness of software

  • Phases

    • Unit testing

      • To test each module (unit, or component) independently

      • Mostly done by developers of the modules

    • Integration and system testing

      • To test the system as a whole

      • Often done by separate testing or QA team

    • Acceptance testing

      • To validate system functions for (and by) customers or user

What is unit testing
What Is Unit Testing?

  • Definition

    • Testing is the process of showing that a program works for certain inputs.

    • A unit is a module or a small set of modules.

      • In Java, a unit is a class or interface, or a set of them, e.g.,

      • An interface and 3 classes that implement it, or

      • A public class along with its helper classes.

    • Unit testing is testing of a unit.


  • Do you get more confidence by running more test data?

Why unit testing
Why Unit Testing?

  • Code isn’t right if it’s not tested.

  • Practical

    • Most programmers rely on testing, e.g.,

      Microsoft has 1 tester per developer.

    • You could get work as a tester.

  • Divide-and-conquer approach

    • Split system into units.

    • Debug unit individually.

    • Narrow down places where bugs can be.

    • Don’t want to chase down bugs in other units.

Why unit testing cont
Why Unit Testing? (Cont.)

  • Support regression testing

    • So can make changes to lots of code and know if you broke something.

    • Can make big changes with confidence.

How to do unit testing
How to Do Unit Testing

  • Build systems in layers

    • Starts with classes that don’t depend on others.

    • Continue testing building on already tested classes.

  • Benefits

    • Avoid having to write (test) stubs.

    • When testing a module, ones it depends on are reliable.


  • How does low coupling help testing?

  • How does high coupling hurt it?

Program to test
Program to Test

public final class IMath {


* Returns an integer approximation to the square root of x.


public static int isqrt(int x) {

int guess = 1;

while (guess * guess < x) {



return guess;



Conventional testing
Conventional Testing

/** A class to test the class IMath. */

public class IMathTestNoJUnit {

/** Runs the tests. */

public static void main(String[] args) {










private static void printTestResult(int arg) {

System.out.print(“isqrt(“ + arg + “) ==> “);




Conventional test output
Conventional Test Output

Isqrt(0) ==> 1

Isqrt(1) ==> 1

Isqrt(2) ==> 2

Isqrt(3) ==> 2

Isqrt(4) ==> 2

Isqrt(7) ==> 3

Isqrt(9) ==> 3

Isqrt(100) ==> 10

  • What does this say about the code? Is it right?

  • What’s the problem with this kind of test output?


  • Automatic verification by testing program

    • Can write such a test program by yourself, or

    • Use a testing tool such as JUnit.

  • JUnit

    • A simple, flexible, easy-to-use, open-source, and practical unit testing framework for Java.

    • Can deal with a large and extensive set of test cases.

    • Refer to www.junit.org.

Testing with junit
Testing with JUnit

import junit.framework.*;

/** A JUnit test class to test the class IMath. */

public class IMathTest extends TestCase {

/** Tests isqrt. */

public void testIsqrt() {

assertEquals(0, IMath.isqrt(0)); // line 23

assertEquals(1, IMath.isqrt(1));

assertEquals(1, IMath.isqrt(2));

assertEquals(1, IMath.isqrt(3));

assertEquals(2, IMath.isqrt(4));

assertEquals(2, IMath.isqrt(7));

assertEquals(3, IMath.isqrt(9));

assertEquals(10, IMath.isqrt(100));


Testing with junit cont
Testing with JUnit (Cont.)

/** Returns the test suite for this test class. */

public static Test suite() {

return new TestSuite(IMathTest.class);


/** Run the tests. */

public static void main(String[] args) {


// junit.swingui.TestRunner.run(suite());



Compilation and output
Compilation and Output

  • $ javac IMath.java IMathTest.java

  • $ java IMathTest

  • .F

  • Time: 0.02

  • There was 1 failure:

  • testIsqrt(IMathTest)junit.framework.AssertionFailedError: expected:<0> but was:<1>

  • at IMathTest.testIsqrt(IMathTest.java:23)

  • at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

  • at sun.reflect.NativeMeth...

  • at sun.reflect.Delegating...

  • at IMathTest.main(IMathTest.java:17)


  • Tests run: 1, Failures: 1, Errors: 0

  • Question: Is this better? Why?


  • Write a JUnit test class for testing

public class ForYou {

/** Return the minimum of x and y. */

public static int min(int x, int y) { ... }


Exercise cont
Exercise (Cont.)

public class ForYou {

/** Return the minimum of x and y. */

public static int min(int x, int y) { ... }


By filling in the following:

import junit.framework.*;

/** Test ForYou. */

public class ForYouTest extends TestCase {

/** Test min. */

public void testMin() {


// the rest as before …


Some terminology
Some Terminology

  • Definition

    • A test data (or case) for a method M is a pair of (o, args), where

      • o is not null and M can be sent to o,

      • args is a tuple of arguments that can be passed to M.

    • A test data, (o, args), for M succeeds iff o.M(args) behaves as expected.

    • A test data, (o, args), for M fails iff it does not behave as expected.

  • Question

    • Why should o not be null?

    • If M has a bug that is revealed by a test data, does that test data for M succeeds or fails?

Parts of test code
Parts of Test Code

  • Definition

    • The test fixture is the set of variables used in testing.

    • The test driver is the class that runs the tests.

    • The test oracle for a test data is the code that decides success or failure for that test data.

  • Question

    • What in the code we saw so far was the test driver, and the oracle?

    • What difference is there between JUnit testing and non-JUnit testing in what we saw before?

Basic usage of junit
Basic Usage of JUnit

To test a type T:

1. Write a class like:

import junit.framework.*;

/** A JUnit test class for the class T. */

public class TTest extends TestCase {

/** Runs the tests. */

public static void main(String[] args) {



/** Returns the test suite for this test class. */

public static Test suite() {

return new TestSuite(TTest.class);


<test methods go here>


Basic usage of junit cont
Basic Usage of JUnit (Cont.)

2. Compile T.java and TTest.java

$ javac T.java TTest.java

3. Run the JUnit graphical user interface on TTest

$ java junit.swingui.TestRunner TTest


Run the text interface (good from makefiles)

$ java TTest

4. Look at the failures and errors

Naming convention
Naming Convention

  • Test methods start with “test”

    e.g., testIsqrt, testMin

  • Test classes end with “Test”

    e.g., IMathTest, ForYouTest

Assertion methods
Assertion Methods

Method Description

assertEquals(a,b) Test if a is equal to b

assertFalse(a) Test if a is false

assertNotSame(a, b) Test if a and b do not refer to the

identical object

assertNull(a) Test if a is null

assertSame(a,b) Test if a and b refer to the identical


assertTrue(a) Test if a is true

- Static methods defined in junit.framework.Assert

- Variations taking string error messages

More on junit test fixture
More on JUnit -- Test Fixture

  • Sharing test data among test methods

public class TTest extends TestCase {

// other methods here …

protected void setUp() throws Exception {

// initialize test fixture variables.


protected void tearDown() throws Exception {

// uninitialize test fixture variables.


// test fixture variables, i.e., fields shared by several test methods.



public class PointTest extends TestCase {

private Point p; // test fixture variable

protected void setUp() { // initializes text fixture variables

p = new Point(10, 10);


protected void tearDown() { } // clean up text fixture variables

public void testSetX() { // tests SetX


assertEquals(20, p.getX());


public void testSetY() { // tests SetY


assertEquals(30, p.getY());


// template and other test methods here…


More on junit test suite
More on JUnit -- Test Suite

  • Definition

    • A test suite is a set of test methods and other test suites.

  • Test Suite

    • Organize tests into a larger test set.

    • Help with automation of testing.


public class AllTestSuite extends TestCase {

/** Returns the test suite for this test class. */

public static Test suite() {

TestSuite suite = new TestSuite() {

public String toString() {

return "Test suite for Project T";






return suite;


// the rest of methods as before …


More on junit
More on JUnit?

  • Refer to www.junit.org

  • JUnit APIs available from the course Web page