Top 40 JUnit Interview Questions and Answers 2024

JUnit Interview Questions and Answers for experienced professionals from Codingcompiler. These JUnit Interview Questions have been structured extraordinarily to get you familiar with the idea of questions you may experience during your interview. We hope that these interview questions on JUnit will help you to crack your next JUnit job interview.

Table of Contents

JUnit Interview Questions

What is Testing?
What is Unit Testing?
What is JUnit?
What is Manual testing?
What is Automated testing?
What is the difference between manual testing and automated testing?
What are important features of JUnit?
How to install JUnit?
What is a Unit Test Case?
Why does JUnit only report the first failure in a single test?

JUnit Interview Questions and Answers

1. What is Testing?
Testing is the process of checking the functionality of the application whether it is working as per requirements.

2. What is Unit Testing?
Unit testing is the testing of single entity (class or method). Unit testing is very essential to every software company to give a quality product to their customers.

3. What is JUnit?
JUnit is a Regression Testing Framework used by developers to implement unit testing in Java and accelerate programming speed and increase the quality of code.
JUnit is the testing framework, it is used for unit testing of Java code.

JUnit = Java + Unit Testing

4. What is Manual testing?
Executing the test cases manually without any tool support is known as manual testing.

5. What is Automated testing?
Taking tool support and executing the test cases by using automation tool is known as automation testing.

6. What is the difference between manual testing and automated testing?
Manual testing is performed by Human, so it is time-consuming and costly. Automated testing is performed by testing tools or programs, so it is fast and less costly.

Give some disadvantages of manual testing.
Following are some disadvantages of manual testing:

The testing is very time consuming and is very tiring.
The testing demands a very big investment in the human resources.
The testing is less reliable
The testing cannot be programmed.

7. What are important features of JUnit?
Import features of JUnit are:

It is an open source framework.
Provides Annotation to identify the test methods.
Provides Assertions for testing expected results.
Provides Test runners for running tests.
JUnit tests can be run automatically and they check their own results and provide immediate feedback.
JUnit tests can be organized into test suites containing test cases and even other test suites.
JUnit shows test progress in a bar that is green if test is going fine and it turns red when a test fails.
Go through the JUnit Video to get clear understanding of JUnit.

8. How to install JUnit?

Installation steps for JUnit :

Download the latest version of JUnit, referred to below as junit.zip.
Unzip the junit.zip distribution file to a directory referred to as %JUNIT_HOME%.

Add JUnit to the classpath −
set CLASSPATH=%CLASSPATH%;%JUNIT_HOME%\junit.jar

Test the installation by running the sample tests distributed with JUnit (sample tests are located in the installation directory directly, not the junit.jar file).

Then simply type −
java org.junit.runner.JUnitCore org.junit.tests.AllTests

All the tests should pass with an “OK” message. If the tests don’t pass, verify that junit.jar is in the CLASSPATH.

9. What is a Unit Test Case?

A Unit Test Case is a part of code which ensures that the another part of code (method) works as expected. A formal written unit test case is characterized by a known input and by an expected output, which is worked out before the test is executed. The known input should test a precondition and the expected output should test a post condition.

10. Why does JUnit only report the first failure in a single test?
Reporting multiple failures in a single test is generally a sign that the test does too much and it is too big a unit test. JUnit is designed to work best with a number of small tests. It executes each test within a separate instance of the test class. It reports failure on each test.

Basic JUnit Interview Questions and Answers

11. In Java, assert is a keyword. Won’t this conflict with JUnit’sassert() method?
JUnit 3.7 deprecated assert() and replaced it with assertTrue(), which works exactly the same way. JUnit 4 is compatible with the assert keyword. If you run with the -ea JVM switch, assertions that fail will be reported by JUnit.

12. When are the unit tests pertaining to JUnit written in Developmental Cycle?
The unit tests are written before the development of the application. It is so because by writing the check before coding, it assists the coders to write error-free codes which further boosts the viability of the form.

13. Shed light on the variety of JUnit classes and make a proper list of them
The JUnit classes are essential classes that are usually utilized in testing and writing the JUnits. Here is the list of the critical JUnit test classes.

Test Suite: It is also known as a composition of various tests
Assert: It is a set of assertive procedures used to design an application
Test Result: It is associated with the collection of results while executing a test case
Test Case: It is that kind of a JUnit class which is related to various fixtures. It also has the ability to run on a variety of tests

14. What is Junit Test Fixture?
A test fixture is a fixed state of a set of objects used as a baseline for running tests. Their purpose is to ensure that there is a well known and fixed environment in which tests are run so that results are repeatable. Examples of fixtures:

Loading a database with a specific, known set of data Copying a specific known set of files
Preparation of input data and setup/creation of fake or mock objects. If a group of tests shares the same fixtures, you should write a separate setup code to create the common test fixture. If a group of tests requires different test fixtures, you can write code inside the test method to create its own test fixture.

15. What are the critical fixtures of JUnit?
The JUnit test framework is associated with the providence of these critical features. They are as follows:

Test Suites
JUnit Classes
Fixtures
Test Runners

16. What do you understand by a fixture?
The fixture is a set of objects of a fixed state that is used as a baseline for running tests. The objective of a test fixture is to make sure that there is a well known and fixed environment to run tests so that results can be repeated. It includes the following two methods −

setUp() method – it runs before every test is called.
tearDown() method – it runs after every test method is called.

17. Name some Junit extensions?
Following are some of the JUnit extensions −

Cactus
JWebUnit
XMLUnit
MockObject

18. What do you understand by JWebUnit? And what are its advantages?
This is the most popular Junit Interview Questions asked in an interview. WebUnit is also a Java-based testing framework to test web applications. It wraps around existing testing frameworks to allow quick testing of web applications and comes with a unified, simple testing interface.
To verify the correctness of an application, JWebUnit provides a high-level Java API to test a web application along with a set of assertions. This includes navigation through links and forms entry and submission. It also involves validation of table contents and other usual business web application features.The easy navigation methods that come with ready-to-use assertions allow for more rapid test creation than using Junit or HtmlUnit only. And if switching from HtmlUnit to other plugins such as Selenium are needed there should be no need to rewrite tests.

19. What is @Test and where it’s used?

@Test annotation is used to mark a method as test method, result of which is then compared with expected output to check whether the test is successful or not.

20. What is @Before and @BeforeClass and it’s usage?

@Before annotation:

syntax:
@Before
public void myMethod()

This method should execute before each test. Such methods are generally used for initialization before performing a actual test in test environment.

@BeforeClass annotation:

syntax:
@BeforeClass
public static void myMethod()

This method should execute before all the tests. It executes only once. Method should be declared static. Mostly used for database connectivity tasks before execution of any of the test.

Advanced JUnit Interview Questions and Answers For Experienced

21. How will you run JUnit from command window?

To run JUnit tests from a command window, you need to check the following list:

Make sure that JDK is installed and the “java” command program is accessible through the PATH setting. Type “java -version” at the command prompt, you should see the JVM reports you back the version string.
Make sure that the CLASSPATH is defined as shown in the previous question.
Invoke the JUnit runner by entering the following command:

java org.junit.runner.JUnitCore

22. How @Test annotation is used for testing exceptions?

@Test (expected = Exception.class)

Limitation: It is used for testing only a single exception.

23. How to write a simple Junit test class?

To write a test case, follow these steps:

Define a subclass of TestCase.
Override the setUp() method to initialize object(s) under test.
Optionally override the tearDown() method to release object(s) under test.
Define one or more public testXYZ() methods that exercise the object(s) under test and assert expected results.

24. What are the top advantages of writing unit tests?
The advantages of writing unit tests include Design testability, Code testability and Code maintainability as good unit tests enforces Object Oriented principles such as Single Responsibility etc. which enables people to avoid code smells such as long classes, long methods, large conditionals etc.

25. How is code cyclomatic complexity related to unit tests?
As code cyclomatic complexity is determined based on number of decision points within the code and hence execution paths, higher cyclomatic complexity makes it difficult to attain achieve test/code coverage.

26. What is mocking and stubbing? Did you use any mocking framework?
Mocking is a feature where an object mimics like a real object. Stubbing are codes that are responsible for taking place of another component.
There are various different Java mocking frameworks such as Mockito, EasyMock etc.

27. In SDLC, When is the right time to start writing unit tests?
Test-along if not test-driven; Writing unit tests towards end is not very effective. Test-along technique recommends developers to write the unit tests as they go with their development.

28. Write a sample unit testing method for testing exception named as IndexOutOfBoundsException when working with ArrayList?

@Test(expected=IndexOutOfBoundsException.class)
public void outOfBounds() {
new ArrayList().get(1);
}

29. Write a sample unit testing method for testing timeout? @Test(timeout=100)
public void infinity() {
while(true);
}

30. Name some code smells which makes it hard to achieve high code coverage?
Long method, Large conditionals

The Best JUnit Interview Questions and Answers

31. What are the different methods of exception handling in JUnit?
There are different ways of exception handling in JUnit. Try catch idiom.
Using JUnit rule.
@Test annotation.
Using catch exception library.
Using customs annotation.

32. How do I execute JUnit from command line?
Executng Junit from command line involves 2 steps. set the ClassPath to include JUnit core libraries. set CLASSPATH=%CLASSPATH%;%JUNIT_HOME%junit.jar
2.Invoke JunitCore. java org.junit.runner.JUnitCore

33. How do I test a private method?
The private methods cannot be tested as any private method only be accessed within the same class. The private method need to tested manually or be converted to protected method.

34. What happens if a test method throws an exception?
The JUnit runner will declare that test as fail when the test method throws an exception.

35. The methods Get () and Set () should be tested for which conditions?
Unit tests performed on java code should be designed to target areas that might break. Since the set() and get() methods on simple data types are unlikely to break, there is no need to test them explicitly. On the other hand, set() and get() methods on complex data types are vulnerable to break. So they should be tested.

36. What is JUnit parameterized test?
The parameterized test is a new feature introduced in JUnit 4. It provides the facility to execute the same test case again and again with different values.

37. Name the tools with which JUnit can be easily integrated.

JUnit Framework can be easily integrated with either of the followings − Eclipse
Ant
Maven.

38. Difference between Assert and Verify ?

Assert works only if assertions ( -ea ) are enabled which is not required for Verify. Assert throws an exception and hence doesn’t continue with the test if assert evaluates to false whereas it’s not so with Verify.

39. Place the JUnit program in the context of the current evolution of tech and programming.
Junit is known as a waning testing framework. It is extensively utilized by developers to carry out unit testing in Java. At the same time, it is also commonly used to speed up applications based in Java. It is crucial to note that, through a consideration of the source code, the application would be efficiently sped up.

40. How to Run Your JUnit 4.4 Tests with a JUnit 3.8 Runner? junit.framework.JUnit4TestAdapter class included in JUnit 4.4 JAR file. Here is sample code:

import junit.framework.Test;
import junit.textui.TestRunner;
import junit.framework.JUnit4TestAdapter;

public class JUnit3Adapter {
public static void main (String[] args) {
Test adaptedTest = new JUnit4TestAdapter(HelloTest.class);
TestRunner.run(adaptedTest);
}
}

Classes junit.framework.Test, junit.textui.TestRunner and junit.framework.JUnit4TestAdapter are included in the JUnit 4.4 JAR file. You don’t need to include the JUnit 3.8 JAR file in your CLASSPATH

JUnit Interview Questions and Answers

JUnit Interview Questions

JUnit Interview Questions and Answers

Basic JUnit Interview Questions and Answers

Advanced JUnit Interview Questions and Answers For Experienced

The Best JUnit Interview Questions and Answers

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