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Overview
JUnit is a Java framework for performing unit tests on code. By testing code after every change, programmers can be reassured that changing a small amount of code does not break the larger system.
Without automated testing tools like JUnit, retesting can be a tedious and inaccurate process. By allowing the testing process to occur frequently and automatically, you can keep software coding errors at a minimum.
Creating the test cases, however, can be a difficult process requiring knowledge of exactly what the code does and how it should perform. You must carefully create the unit tests performed by JUnit to ensure that the tests rigorously check the code just as it would run in the real world. In this article, we first look at how to create unit tests and then at how to put together test suites.
Contents:
* Introduction
* What is JUnit?
* Installation
* Testing using JUnit
* Creating Test Cases
* What is a TestSuite?
* How to create unit tests with JUnit?
* Example
JUnit is a Java framework for performing unit tests on code. By testing code after every change, programmers can be reassured that changing a small amount of code does not break the larger system.
Without automated testing tools like JUnit, retesting can be a tedious and inaccurate process. By allowing the testing process to occur frequently and automatically, you can keep software coding errors at a minimum.
Creating the test cases, however, can be a difficult process requiring knowledge of exactly what the code does and how it should perform. You must carefully create the unit tests performed by JUnit to ensure that the tests rigorously check the code just as it would run in the real world. In this article, we first look at how to create unit tests and then at how to put together test suites.
Contents:
* Introduction
* What is JUnit?
* Installation
* Testing using JUnit
* Creating Test Cases
* What is a TestSuite?
* How to create unit tests with JUnit?
* Example
Introduction
JUnit is a framework for implementing testing in Java.
It provides a simple way to explicitly test specific areas of a Java program, it is extensible and can be employed to test a hierarchy of program code either singularly or as multiple units.
Why use a testing framework? Using a testing framework is beneficial because it forces you to explicitly declare the expected results of specific program execution routes. When debugging it is possible to write a test which expresses the result you are trying to achieve and then debug until the test comes out positive. By having a set of tests that test all the core components of the project it is possible to modify specific areas of the project and immediately see the effect the modifications have on the other areas by the results of the test, hence, side-effects can be quickly realized.
JUnit promotes the idea of first testing then coding, in that it is possible to setup test data for a unit which defines what the expected output is and then code until the tests pass. It is believed by some that this practice of "test a little, code a little, test a little, code a little..." increases programmer productivity and stability of program code whilst reducing programmer stress and the time spent debugging.
JUnit is a framework for implementing testing in Java.
It provides a simple way to explicitly test specific areas of a Java program, it is extensible and can be employed to test a hierarchy of program code either singularly or as multiple units.
Why use a testing framework? Using a testing framework is beneficial because it forces you to explicitly declare the expected results of specific program execution routes. When debugging it is possible to write a test which expresses the result you are trying to achieve and then debug until the test comes out positive. By having a set of tests that test all the core components of the project it is possible to modify specific areas of the project and immediately see the effect the modifications have on the other areas by the results of the test, hence, side-effects can be quickly realized.
JUnit promotes the idea of first testing then coding, in that it is possible to setup test data for a unit which defines what the expected output is and then code until the tests pass. It is believed by some that this practice of "test a little, code a little, test a little, code a little..." increases programmer productivity and stability of program code whilst reducing programmer stress and the time spent debugging.
What is JUnit?
JUnit is a simple open source Java testing framework used to write and run repeatable automated tests.
It is an instance of the xUnit architecture for unit testing framework. Eclipse supports creating test cases and running test suites, so it is easy to use for your Java applications.
JUnit features include:
* Assertions for testing expected results
* Test fixtures for sharing common test data
* Test suites for easily organizing and running tests
* Graphical and textual test runners
JUnit is a simple open source Java testing framework used to write and run repeatable automated tests.
It is an instance of the xUnit architecture for unit testing framework. Eclipse supports creating test cases and running test suites, so it is easy to use for your Java applications.
JUnit features include:
* Assertions for testing expected results
* Test fixtures for sharing common test data
* Test suites for easily organizing and running tests
* Graphical and textual test runners
Installation
It is assumed that you know how to setup environment variables and install software on your operating system,
for a comprehensive guide to doing so for Windows see Configuring A Windows Working Environment, for Unix see Configuring A Unix Working Environment Follow these instructions to install JUnit:
1. Download the latest version of JUnit from http://download.sourceforge.net/junit/
2. Uncompress the zip to a directory of your choice.
3. Add /path/to/whereyouextractedjunit/junit/junit.jar to your Java CLASSPATH environment variable.
Testing using JUnit
While compilers can look for structural problems in a program, they cannot tell whether the results of a program or method are correct.
Instead, all developers test their programs to ensure that they behave as expected. This can be as simple as calling a method in the Interactions Pane to view its results, but this technique requires you to think about the answers you expect every time you run any tests. A much better solution is to give the tests the answers you expect, and let the tests themselves do all the work.
Thankfully, a technique known as unit testing makes this quite easy. You write many small tests that create your objects and assert that they behave the way you expect in different situations. A unit test framework known as JUnit (http://www.junit.org) automates the process of running these tests, letting you quickly see whether your program returns the results you expect.
DrJava makes the process of running unit tests very simple by providing support for JUnit. Once you have written a JUnit test class (as described in the next section), you can simply choose the "Test Current Document" command from the Tools menu to run the tests and view the results. The name of the tests being run will be shown in the Test Output tab, with each test method turning green if it completes successfully and red if it fails. Any failures will be displayed after the list of methods in the same way as the compiler errors. A progress bar will keep you updated on how many tests have been run.
Also, clicking the "Test" button on the toolbar or choosing "Test All Documents" from the Tools menu will run JUnit on any open testcases, making running multiple test files very simple.
Creating Test Cases
Test cases for JUnit are written as Java classes that extend the JUnit framework. These classes have a number of methods, each of which tests a particular function, or unit, of the code.
For example, for a simple accounting product, one test might cover logging in with a username and password. A second might check depositing an amount of money and ensure the balance increased by the same amount. A third test might mimic withdrawing money from an account. Generally, the more test cases you write, the more thorough the test will be overall. You should test every functional area of a product: Only by doing this will the tests be of real value in making sure that small changes in one place do not have larger implications in another.
Creating a new test case is easy. This class must extend the TestCase class and have a constructor that calls the constructor of the base class.
This class is called the test harness, and it’s where you write your tests. Each time a test is called, JUnit will execute the setUp() method for you to initialize any values you need. Next, it will call a test case and then call tearDown() to undo the initialization and go on to the next test.
This simple test harness contains two tests, testBooleanTrue() and testBooleanFalse(). Each test must be declared public and must make a call to JUnit to inform JUnit of the status of the test. In this case, we force one test to always succeed and the other to always fail.
It is assumed that you know how to setup environment variables and install software on your operating system,
for a comprehensive guide to doing so for Windows see Configuring A Windows Working Environment, for Unix see Configuring A Unix Working Environment Follow these instructions to install JUnit:
1. Download the latest version of JUnit from http://download.sourceforge.net/junit/
2. Uncompress the zip to a directory of your choice.
3. Add /path/to/whereyouextractedjunit/junit/junit.jar to your Java CLASSPATH environment variable.
Testing using JUnit
While compilers can look for structural problems in a program, they cannot tell whether the results of a program or method are correct.
Instead, all developers test their programs to ensure that they behave as expected. This can be as simple as calling a method in the Interactions Pane to view its results, but this technique requires you to think about the answers you expect every time you run any tests. A much better solution is to give the tests the answers you expect, and let the tests themselves do all the work.
Thankfully, a technique known as unit testing makes this quite easy. You write many small tests that create your objects and assert that they behave the way you expect in different situations. A unit test framework known as JUnit (http://www.junit.org) automates the process of running these tests, letting you quickly see whether your program returns the results you expect.
DrJava makes the process of running unit tests very simple by providing support for JUnit. Once you have written a JUnit test class (as described in the next section), you can simply choose the "Test Current Document" command from the Tools menu to run the tests and view the results. The name of the tests being run will be shown in the Test Output tab, with each test method turning green if it completes successfully and red if it fails. Any failures will be displayed after the list of methods in the same way as the compiler errors. A progress bar will keep you updated on how many tests have been run.
Also, clicking the "Test" button on the toolbar or choosing "Test All Documents" from the Tools menu will run JUnit on any open testcases, making running multiple test files very simple.
Creating Test Cases
Test cases for JUnit are written as Java classes that extend the JUnit framework. These classes have a number of methods, each of which tests a particular function, or unit, of the code.
For example, for a simple accounting product, one test might cover logging in with a username and password. A second might check depositing an amount of money and ensure the balance increased by the same amount. A third test might mimic withdrawing money from an account. Generally, the more test cases you write, the more thorough the test will be overall. You should test every functional area of a product: Only by doing this will the tests be of real value in making sure that small changes in one place do not have larger implications in another.
Creating a new test case is easy. This class must extend the TestCase class and have a constructor that calls the constructor of the base class.
This class is called the test harness, and it’s where you write your tests. Each time a test is called, JUnit will execute the setUp() method for you to initialize any values you need. Next, it will call a test case and then call tearDown() to undo the initialization and go on to the next test.
This simple test harness contains two tests, testBooleanTrue() and testBooleanFalse(). Each test must be declared public and must make a call to JUnit to inform JUnit of the status of the test. In this case, we force one test to always succeed and the other to always fail.
JUnit