Junit Testing Tutorial For Beginners

Introduction

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This tutorial will help the software testing aspirants with the usage of JUnit in unit testing while working with Java. The tutorial is designed for beginners to help them understand the basic functionality of JUnit.

What is JUnit?

It is a unit testing framework for the Java programming language. JUnit has been crucial in the development of test-driven development and is one of a family of unit testing frameworks. The primary usage of JUnit is to write repeatable tests for your application code units. JUnit stimulates the idea of “testing first, then coding,” which accentuates on setting up of the test data for the code snippets that can be tested first and then implemented. The test approach explicates –

test a little + code a little = JUnit

JUnit increases the productivity of a programmer and the stability of the program’s code snippets, which reduces the time of the tester, which is spent on debugging of the code.

Features of JUnit

• It is an open-source framework that is used for writing and running tests
• It provides annotations to identify test methods
• It provides assertions for testing the expected results
• It provides test runners to run tests
• It allows the tester to write code faster which increases the quality
• These tests are run automatically, check their results, and provide immediate feedback
• These show test progress in a green color bar if the test is running smoothly, and it turns red if the test fails

How to Download and Install JUnit

Local Environment Setup

JUnit is a framework for Java, so the very first requirement is to have JDK installed on your machine.

System Requirements

JUnit Test Framework

JUnit is a Regression testing framework that is used by developers to implement unit testing in Java to escalate the speed of programming and elevate the quality of code. The JUnit framework also allows quick and easy generation of test data and test cases.

The JUnit test framework provides the following important features:-

• Test Fixtures
• Test Suites
• Test Runners
• JUnit Classes

Test Fixtures

A fixture is a fixed state of a set of objects which is used as a baseline for running the test cases. The primary purpose of a test fixture is to fortify that there is a well-known and fixed environment in which tests are run so that results are in repeated manner.

• setUp() method runs before every test invocation. The annotation @Before is used
• tearDown() method and runs after every test method. The annotation @After is used

The below code will execute two test cases on a simple file.

public class TestCaseFile

{

private File output;

output = new File(...);

output.delete();

public void testFile1()

{

//Code to verify Test Case 1

}

output.delete();

output = new File(...);

public void testFile2()

{

//Code to verify Test Case 2

}

output.delete();

}

There are few issues in the above code-

• The code is not readable
• The code is not easy to maintain
• When the test suite will be complex, the code will contain logical issues

Let’s compare the same code using JUnit-

public class TestCaseFile

{

private File output;

@Before public void createOutputFile()

{

output = new File(...);

}

@After public void deleteOutputFile()

{

output.delete();

}

@Test public void testFile1()

{

// code for test case objective

}

@Test public void testFile2()

{

// code for test case objective

}

}

The code is now readable and maintainable. The above code structure is Text fixture.

Test Suites

To execute multiple test cases in a specific order, it is done by combining all the test cases in a single origin. The origin is known as test suites.

To run the test suite, you need to annotate a class using the annotations mentioned below-

• @Runwith(Suite.class)
• @SuiteClassses(test1.class,test2.class……) or @SuiteClasses({test1.class,test2.class})

Below example will run the TestJUnit1.class and TestJUnit2.class

import org.JUnit.runner.RunWith;

import org.JUnit.runners.Suite;

//JUnit Suite Test

@RunWith(Suite.class)

@Suite.SuiteClasses({ 

   TestJUnit1.class ,TestJUnit2.class

}) 

public class JUnitTestSuite {

}

Test Runners

The Test Runner is used to execute the test cases. Let’s take an assumption of the test cases class TestJUnit.

import org.JUnit.runner.JUnitCore;

import org.JUnit.runner.Result;

import org.JUnit.runner.notification.Failure; 

public class TestRunner {

   public static void main(String[] args) {

      Result result = JUnitCore.runClasses(TestJUnit.class);

      for (Failure failure : result.getFailures()) {

         System.out.println(failure.toString());

      }

      System.out.println(result.wasSuccessful());

   }

}

JUnit Classes

There are important classes which are used in writing and testing JUnits. Some of them are-

• Assert: It contains a set of assert methods
• TestCase: It contains a test case that defines the fixture to run multiple tests
• TestResult: It contains methods to collect the results of executing a test case

JUnit Annotations & API

An annotation is a special form of meta-data in a syntactical manner that can be added to Java source code for the better readability and structure. Variables, parameters, packages, methods, and classes can be annotated. JUnit offers the following annotations to write tests:

Following is the execution order of the above-mentioned methods when a JUnit4 test is run: -

1. A method annotated with @BeforeClass
2. A method annotated with @Before
3. A first method annotated with @Test, i.e., test1().
4. A method annotated with @After
5. A method annotated with @Before
6. A second method annotated with @Test, i.e., test2().
7. A method annotated with @After
8. A method annotated with @AfterClass

JUnit Parameterized Test

JUnit Parameterized test was the new feature that was introduced in JUnit 4. This allows the developer to run the same test, again using different values. A total of five steps are followed to create a parameterized test: -

• Annotate test class with @RunWith(Parameterized.class).
• Create a public static method annotated with @Parameters that returns a Collection of Objects (as Array) as test data set.
• Create a public constructor that takes in what is equivalent to one "row" of test data.
• Create an instance variable for each "column" of test data.
• Create your test case(s) using the instance variables as the source of the test data.

Let’s look into an example.

Create another class TestRunner to compile the program.

import org.JUnit.runner.JUnitCore;

import org.JUnit.runner.Result;

import org.JUnit.runner.notification.Failure;

public class Runner

{

public static void main(String[] args)

{

Result result = JUnitCore.runClasses(PrimeNumberCheckerTest.class);

for (Failure failure : result.getFailures())

{

System.out.println(failure.toString());

}

System.out.println(result.wasSuccessful());

}

}

Output 

Parameterized Number is: 2
Parameterized Number is : 6
Parameterized Number is : 19
Parameterized Number is : 22
Parameterized Number is : 23
true

JUnit ErrorCollector

Normally when you identify an error during execution of the test, you would stop the test, fix the error, and re-run the test. But in the case of JUnit, you can continue with the test execution even when you find an issue or the test fails. ErrorCollector collects all error objects and reports them only once after the test execution is over.

While writing a test script, if you want to execute all the tests even if any line of code fails due to any network failure or any other reason, in that situation, you can continue executing the test script by using a special feature provided by JUnit, which is called ‘error collector.’

JUnit uses @Rule annotation, which is used to create an object of error collector. Once the object is created, you can easily add all the errors into the object using the method addError (Throwable error). Throwable is a superclass of Exception and Error class in Java. When errors are added in this way, these errors will be logged in a JUnit test result.

The major benefit of adding all the errors in an ErrorCollector is that you can verify all the errors at once. And, if the script fails in the middle, it can continue executing it. But yes, it is important to note here that in the case of a try/catch block, using ErrorCollector won’t be possible.

JUnit Exception Test

JUnit provides the exception handling of code. You can test whether the code throws a desired exception or not. There are three different ways to test that a method would throw the expected exception:-

1. Set the expected parameter @Test(expected = FileNotFoundException.class).

@Test(expected = FileNotFoundException.class) 

    public void testReadFile() throws IOException { 

        FileReader reader = new FileReader("test.txt");

        reader.read();

        reader.close();

    }

2. Using try-catch

@Test

    public void testReadFile2() { 

        try {

            FileReader reader = new FileReader("test.txt");

            reader.read();

            reader.close();

            fail("Expected an IOException to be thrown");

        } catch (IOException e) {

            assertThat(e.getMessage(), is("test.txt (No such file or directory)"));

        }                 

    }

3. Testing with ExpectedException Rule.

@Rule

    public ExpectedException thrown = ExpectedException.none();

@Test

    public void testReadFile3() throws IOException {                

        thrown.expect(IOException.class);

        thrown.expectMessage(startsWith("test.txt (No such file or directory)"));

 FileReader reader = new FileReader("test.txt");

        reader.read();

        reader.close();

    }

JUnit Ignore Test

In case of the failure of the test case, the @Ignore annotation helps. A test method annotated with @Ignore will not be executed. Also, if a test class is annotated with @Ignore, then none of its test methods will be executed.

Let’s see the JUnit Ignore test into an action-

package com.mkyong;

import org.JUnit.Ignore;

import org.JUnit.Test;

import static org.hamcrest.CoreMatchers.is;

import static org.JUnit.Assert.assertThat;

public class IgnoreTest {

    @Test

    public void testMath1() {

        assertThat(1 + 1, is(2));

    }

    @Ignore

    @Test

    public void testMath2() {

        assertThat(1 + 2, is(5));

    }

    @Ignore("some one please create a test for Math3!")

    @Test

    public void testMath3() {

        //...

    }

}

In the above code snippet, both testMath()2 and testMath3() will be ignored.

Writing Tests in JUnit

In JUnit, test methods are marked with @Test annotation. To run the method, JUnit first constructs a fresh instance of the class and then invokes the annotated method. JUnit will report any exceptions thrown by the test as a failure. If no exceptions are thrown, the test is assumed to have succeeded.

JUnit Test Suites

Using JUnit test suites, you can run tests spread into multiple test classes. In JUnit, both @RunWith and @Suite annotations are used to run the suite tests.

JUnit Assertions

Assertions help in validating the expected output with the actual output of a test case. All the assertions are in the org.JUnit.Assert class. All assert methods are static, it enables better readable code. JUnit 4 has a set of following assertions: -

• org.JUnit.Assert.assertArrayEquals
• org.JUnit.Assert.assertEquals
• org.JUnit.Assert.assertFalse
• org.JUnit.Assert.assertNotNull
• org.JUnit.Assert.assertNotSame
• org.JUnit.Assert.assertNull
• org.JUnit.Assert.assertSame
• org.JUnit.Assert.assertTrue

the org.JUnit.Assert.assertThat method (available in JUnit4) which uses matchers and is better than old style assertions because it provides:

• Better readability

  • assertThat(actual, is(equalTo(expected))); is better than assertEquals(expected, actual);
  • assertThat(actual, is(not(equalTo(expected)))); is better than assertFalse(expected.equals(actual));

• Better failure messages

  • java.lang.AssertionError: Expected: is "hello" but: was "hello world" is better than org.JUnit.ComparisonFailure: expected: but was:

• Flexibility

  • Multiple conditions could be asserted using matchers like anyOf or allOf.

JUnit Assumptions

Assumptions indicate the conditions in which a test is meaningful. A failed assumption does not mean the code is broken but that the test provides no useful information. Assumptions basically mean “don’t run this test if these conditions don’t apply.” The default JUnit runner skips tests with failing assumptions.

Summary

JUnit is a unit testing framework for Java programming language. With this tutorial, you might have understood the basics of JUnit and How to Download and Install JUnit, JUnit Test Framework, JUnit Annotations & API, JUnit Parameterized Test, JUnit ErrorCollector, JUnit Exception Test, JUnit Ignore Test, Writing Tests in JUnit, JUnit Test Suites, JUnit Assertions, JUnit Assumptions and scaled your unit testing practice like a pro. If not done yet, talk to our counselors at JanBask Training to learn more about QA Testing. Join our Online Certification Courses for Quality Assurance, which will help you broaden your knowledge based on QA techniques and improve your Software QA Tester resume. In order to meet QA experts who can help you improve your testing skills, join our QA Testing Community & Forum. 

Happy Testing! 

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