38 Common JUnit Interview Questions (With Sample Answers)

By Indeed Editorial Team

Published 11 May 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

During an interview for a web developer, systems engineer or software tester position, the hiring manager may ask a candidate about their code-testing experience with the JUnit open-source platform. Since many technology companies use this platform, they often prefer candidates with JUnit testing experience. By understanding the types of technical questions you could encounter during a JUnit interview, you can prepare well and improve your chances of getting selected for the job. In this article, we provide a list of frequently asked JUnit interview questions and offer some sample answers to help you with your job interview preparation.

General JUnit interview questions

Interviewers may ask you the following JUnit interview questions to assess your personality and level of articulacy:

  1. What are your long-term career goals?

  2. How do you decide your work priorities?

  3. What unique qualities might a coder have?

  4. On a scale of one to 10, how would you rate your coding skills?

  5. What is your preferred communication style?

  6. What do you know about JUnit?

  7. What can you tell me about unit testing?

  8. What do you know about code testing?

  9. How does manual testing differ from automated testing?

  10. What is a test suite?

Related: Coder Vs Programmer - Fundamental Differences

Questions about your background and experience

You can expect some of the following interview questions about your educational background and work experience:

  1. What made you decide to take up unit testing?

  2. Do you have a Java certification?

  3. Do you have a JUnit certification?

  4. How would you install JUnit?

  5. Have you ever written a JUnit test case?

  6. Can you tell me about parameterised tests?

  7. When was the last time you performed manual testing?

  8. How do you use a mocking framework?

  9. Have you ever used the protected method for testing?

  10. What can you learn from test results?

Related: 40 Manual Testing Interview Questions (With Example Answers)

In-depth questions for a JUnit interview

During the job interview, the interviewer may ask you the following in-depth questions to test your understanding of JUnit testing and frameworks:

  1. What are some JUnit extensions that you've worked with?

  2. Can you list some JUnit classes?

  3. Can you list the annotations in JUnit and their purpose?

  4. What are the methods to handle exceptions in JUnit?

  5. Do you know the @Ignore test in JUnit?

  6. How would you run JUnit from the command line?

  7. What do you know about the key components of Cactus?

  8. What do you know about JUnitCore class?

  9. Why do you use JUnit for testing your code?

  10. What is the difference between setUp() and tearDown()?

Related: Technical Interview Questions And Example Answers

JUnit interview questions with sample answers

The following JUnit interview questions with sample answers may help you prepare for your upcoming job interview:

1. Who uses JUnit, and what are the benefits of using it?

By asking this question, the interviewer wants to find out if you understand the purpose of the JUnit testing framework. Your response can demonstrate your understanding of the different technical roles in a software development company and the benefits of using JUnit.

Example: 'Software developers generally use the JUnit testing framework when they develop new software. It enables them to check the code periodically as they work. The quality assurance engineers also test the software while they're developing it. They often use manual testing methods. The great benefit of using JUnit for testing purposes is that you can automate it, which ensures quick testing. Additionally, you can reuse the test codes and easily undertake regression testing.'

2. What are the important features of JUnit?

Interviewers may ask this question to test your understanding of JUnit. If the available job position requires you to work in JUnit, it's important for the Interviewers to find out whether you're familiar with its different features. You can explain these briefly in your answer.

Example: 'One of the most important features of JUnit is that it's an open-source framework. You can verify different testing methods using the annotation that JUnit provides, and you can test your expected results with its assertions. Similarly, JUnit includes test runners to conveniently verify your work. JUnit also allows for automation, which is convenient for checking large-scale results and receiving feedback. You can also organise the tests into test suites that contain test cases and other test suites while checking the status of the JUnit by following the red and green indicators, which denote failure or success, respectively.'

3. What do you know about manual and automated testing?

When interviewers ask this question, they typically want to assess your knowledge of different testing methods. You can begin by mentioning that a programme's specific requirements may necessitate different testing methods. You can then briefly describe the uses of manual and automated testing strategies.

Example: 'The testing methods I use depend on the product I am testing. When I test products with short life cycles or new products that the company has not yet released onto the market, I use manual testing to check that the code is correct. You do not necessarily require in-depth knowledge of coding to do manual testing. Typically, anyone can do it. You can test the code more quickly and efficiently using automated testing, but it's often necessary to have correct test scripts to check the code for the required criteria.'

Related: Guide To Software Testing Careers (Skills And Salary)

4. Do you know the difference between JUnit and TestNG?

You may encounter this question during many interviews for software testing jobs. Interviewers often ask it to gauge your understanding of different testing frameworks. You can list a few differences between JUnit and TestNG in your answer.

Example: 'There are differences between JUnit and TestNG. JUnit uses a complicated naming convention for annotations, such as "Before", "After" and "Expected". The annotations in TestNG are comparatively simpler, such as "BeforeMethod", "AfterMethod" or "ExpectedException". JUnit requires you to follow specific styles like @BeforeClass and @AfterClass for method declarations, while there are no such restrictions with TestNG. You can group test cases in TestNG unlike in JUnit, and in contrast to JUnit, TestNG generally allows you to rerun failed tests.'

5. What do you learn by unit testing in JUnit?

Since the principle of unit testing is important in software development, you can expect this question during the job interview. In your answer, you can explain what unit testing is and its purpose in JUnit.

Example: 'When you isolate and test the smallest piece of code in the system, it's known as unit testing. The smallest code in most software programs can be a function, a method, a subroutine or a property. Unit testing is important in JUnit as it can help you to check and uphold the quality of software products during their development. You can use unit testing to carry out regression testing and reproducible automated tests.'

6. What do you do to handle exceptions?

It's important for testers to know how to handle exceptions, since test exceptions are common in JUnit. When the interviewer asks this question, you can explain why test exceptions occur. You can also give an example to demonstrate your experience.

Example: 'The first thing I do is find out if the exception was a planned one. Checking the code can help identify that. JUnit can handle exceptions, but unplanned exceptions usually occur because there is a mistake in the code. So, after checking the code, I can find and correct the issue. I usually check the test result using @Test annotation.'

7. Does JUnit understand which classes it tests?

An interviewer may ask this question to test your knowledge of navigating the JUnit test framework. In your response, you can mention the different types of available classes. You can also describe the method you might use to enter them to ensure the test runs as expected.

Example: 'When you run a test in the JUnit testing framework, the test is a method contained in a class. That class is a test class, and you can only use it for testing purposes. To define a method as a test method, you can annotate it with @Test. Then you can execute the code you want to test to see if it succeeds.'

8. How do you prepare code to facilitate testing?

The interviewer may ask this question to test your knowledge of automated testing in JUnit. Your response can demonstrate your knowledge of coding best practices. You can explain how you prepare the code to improve the effectiveness of the automated testing so that the test script can catch all passes and failures.

Example: 'You can make your code more testable by using an interface rather than a concrete class. Then you can use a mock or stub for testing rather than a class. Another best practice for testing is to use a dependency injection. This enables you to test individual parts of code easily. You can supply dependency from the test configuration or create an object to test on the mock or stub. You can also test a class that does not yet have a coded dependency.'

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