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To contribute to this FAQ, simply write a JUnit-related. About. JUnit 5 is the next generation of JUnit. The goal is to create an. This small example shows you how to write a unit test. Create a new folder junit-example and download the current from JUnit’s release page and Hamcrest to this folder. The Java compiler creates a file

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A software test is a piece of software, which executes another piece of software. It validates if that code results in the expected state state testing or executes the expected sequence of events behavior testing.

Software unit tests help the developer to verify that the logic of a piece of the program is correct. Running tests automatically helps to identify software regressions introduced by changes in the source code. Having a high test coverage of your code allows you to continue documentatoin features without having to perform lots of manual tests. The code which is tested is typically called the code under test. If you are testing an application, this is called the application under test.

A test fixture is a fixed state in code which is tested used as input for a test. Another way to describe this is a test precondition. For example, a test fixture might be a a fixed string, which is used as input for a method.

The test would validate if the method behaves correctly with this input. A unit test is a piece of code written by a developer that executes a specific functionality in the code to be tested and asserts a certain behavior or state. A unit test targets a small unit of code, e. External dependencies cocumentation be removed from unit tests, e.

The new major version of the programmer-friendly testing framework for Java

Unit tests are not suitable for testing complex user interface or component interaction. For this, you should develop integration tests. An integration test aims to test the behavior of a component or the integration between a set of components. The term functional test is sometimes used as synonym for integration test. Integration tests check that the whole system works as intended, therefore they are reducing the need for intensive manual tests.

These kinds of tests allow you to translate your user stories into a test suite. The test would resemble an expected user interaction with the application. Performance tests are used to benchmark software components repeatedly. A test is a behavior test also called interaction test if it checks if certain methods were called with the correct input parameters. A behavior test does not validate the result of a method call.

State testing is about validating the result. Behavior testing is about testing the behavior of the application under test. If you are testing algorithms or system functionality, in most cases you may want to test state and not interactions. A typical test setup uses mocks or stubs of related classes to abstract the interactions with these other classes away Afterwards you test the state or the behavior depending on your need.


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There are several testing frameworks available for Java. Typical, unit tests are created in a separate project or separate source folder to keep the test code separate from the real code.

The standard convention from the Maven and Gradle build tools is to use:. What should be tested is a highly controversial topic. Some developers believe every statement in your code should be tested. In any case you should write software tests for the critical and complex parts of your application.

If you introduce new features a solid test suite also protects you against regression in existing code. In general it it safe to ignore trivial code. For example, it is typical jumit4 to write tests for getter and setter methods which simply assign values to fields. Writing tests for these statements documentatipn time consuming and pointless, as you would be testing the Java virtual documenfation.

The JVM itself already has test cases for this. If you are developing end user applications you are safe to assume that a field assignment works in Java. If you start developing tests for an existing code base without any tests, it is good practice to start writing tests for code in which most of the errors happened in the past. This way you can focus on the critical parts of your application. JUnit is a test framework which uses annotations to identify methods that specify a test.

JUnit is an open source project hosted at Github. A JUnit test is a method contained in a class which is only used for testing. This is called a Test class. To define that a certain method is a test method, annotate it with the Test annotation.

This method executes the code under test. You use an assert method, provided by JUnit or another assert framework, to check an expected result versus the actual result.

These method calls are typically called asserts or assert statements. You should provide meaningful messages in assert statements.

That makes it easier for the user to identify and fix the problem. This is especially true if someone looks at the problem, who did not write the code under test or the test code. The following code shows a JUnit test using the JUnit 5 version. This test assumes that the MyClass class exists and has a multiply int, int method. There are several potential naming conventions for JUnit tests. A widely-used solution for classes is to use the “Test” suffix at the end of test classes names.

As a general rule, a test name should explain what the test does. If that is done correctly, reading the actual implementation can be avoided. One possible convention is to use the “should” in the test method name. This gives a hint what should happen if the test method is executed. If you are using the Maven build system, you should use the “Test” suffix for test classes.


The Maven build system via its surfire plug-in automatically documentatio such classes in its test scope. Build systems like Apache Maven or Gradle in combination with a Continuous Integration Server like Jenkins can docmentation used to execute tests automatically on a regular basis.

JUnitCore class provides the runClasses method. This method allows you to run one or several tests classes. As a return parameter you receive an object of the type org. This object can be used to retrieve information about the tests. The following class demonstrates how to run the MyClassTest. This class executes your test class and write doxumentation failures to the console.

This class can be executed like any other Java program on the command line. JUnit assumes that all test methods can be executed in an arbitrary order. Well-written test code should not assume any order, i. As of JUnit 4. You can use an annotation to define that the test methods are sorted by method dockmentation, in lexicographic order. You can also explicitely set the default by using the MethodSorters. You can also use MethodSorters. JUnit uses annotations to mark methods as test methods and to configure them.

The following table gives an overview of the most important annotations in JUnit for the 4. All these annotations can be used on methods. Executed before each test.

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It is used to prepare the test environment e. Executed after each test. It is used to cleanup the test environment e. It can also save memory by cleaning up expensive memory structures. Executed once, before the start of all tests. It is used to perform time intensive activities, for example, to connect to a database. Methods marked with this annotation need to be defined as static to work with JUnit. Executed once, after all tests have been finished. It is used to perform clean-up activities, for example, to disconnect from a database.

Methods annotated with this annotation need to be defined as static to work with JUnit.

Marks that the test should be disabled. This is useful when the underlying code has been changed and the test case has not yet been adapted.

Or if the execution time of this test is too long to be included. Documenration is best practice to provide the optional description, why the test is disabled. JUnit provides static methods to test for certain conditions via the Assert class. These assert statements typically start with assert.

They allow you to specify the error message, the expected and the actual result. An assertion method compares the actual value returned by a test to the expected value.