55+ Junit Interview Questions & Answers To Hire Or Get Hired

JUnit, often referred to as simply "junit," is a java-based testing framework. It is one of the core languages and frameworks used in unit testing. The process of unit testing is primarily used to ensure that web and native applications meet certain user-story criteria in an automated fashion. If you could imagine process of clicking around a website or application and the potential variations that might exist in order to produce a certain feature, it becomes clear that manual testing would be quite time-consuming. Automated unit testing helps to identify and automate certain scenarios. When a feature is built and unit testing occurs, it can either pass or fail. When it fails, it indicates to the developer that something didn't meet the expected events or requirements. This then gives the developer the ability to back through their work and figure out why that particular feature didn't work as a baseline or why it didn't work when potentially merged with the work of multiple different team members. This process often happens before heavy software releases, but it is becoming more common to do on a regular basis, especially since software applications are becoming more and more robust. Below are some common junit interview questions and answers that you can use to study with as you enter your next job interview. As with all answers, I suggest that you take the time to think through how you would frame the answer in your own words and highlighting your own experiences and understanding. This will convey more confidence and help you majorly in the long run.

1. What is Junit?

Junit is a testing framework used for Java programming languages. It is written in Java and has been crucial in the development of test-driven products and codes. A small part of a larger collection of testing frameworks dubbed xUnit, Junit was developed by Erich Gamma and Kent Beck. It assists the developer to write and execute repeatable automated tests. This helps to efficiently automate an otherwise-tedious testing process, which is especially integral to larger interfaces. Junit has also been ported to a number of other languages including PHP, Python, and even C++.

2. Why would you use Junit to test your code?

Junit provides a specific development framework, which allows for the following to occur:

• Junit allows for both early and automated testing.
• The framework allows for the reuse of testing code.
• Junit tests may be integrated with the build meaning, and regression testing can be done at the unit level.
• When there is a transfer Junit, tests may act as documentation for the unit tests.

3. What is unit testing?

Unit testing refers to the process of checking and verifying the functionality nature of the application to determine whether it lives up to the stated requirements.

4. What is the difference between automated and manual testing?

Manual testing is done by people, which means it is often prone to errors, time consuming, and costly. Automated testing, on the other hand, is done by testing tools or programs, making it faster, more efficient, and cheaper.

5. What are the disadvantages that come with manual testing?

• It is time consuming and tedious; because the test cases are done by people, they are usually prone to errors take significant amounts of time.
• Significant investment is directed at human resources; because test cases must be executed by humans, more testers are needed when it comes to manual testing.
• It is non-programmable; there is no real programming that can be done in order to write the sophisticated tests that fetch hidden information.
• It is not very reliable: manual testing is often less reliable because the tests may not be done with precision and errors become more probable the longer a human tester works.

6. What are the main inherent advantages of Automated Testing?

• It is quite fast; automation runs test cases far faster than even the quickest human tester can.
• There is significant cost reduction; humans hired are limited, and the only upfront cost of automated testing comes from the programs and tools themselves.
• They are programmable; testers are able to program sophisticated tests in order to display hidden information.
• They are also more reliable; the automation tests perform the same thing every time, leading to a higher proportion of accuracy than a person could ensure.

7. What are the significant features of a Junit?

• It provides an open-source framework.
• It provides test runners that in turn run the tests.
• It gives assertions concerning the process of testing for expected results.
• The JUnit tests may be run automatically, periodically checking results and allowing for immediate feedback.
• The JUnit tests may be organized according to test suites, which have test cases, and then other suites.
• The JUnit reveals test progress using a convenient and user-friendly bar that is green if the test is successful and red if there is failure.

8. What is a unit test case?

It is part of a code that makes certain that another part of code works as should be expected. In order for one to achieve these results in a quick fashion, the test framework is necessary. JUnit presents itself as the perfect unit test framework for Java.

9. What are the best practices to write a unit test case?

A unit test case, which is formally written using both a known input and an expected output, is worked out before the execution of the test. The known input should be able to test a precondition and the expected output ought to test the post-condition. There have to be at least two unit test cases for each need. These would be one positive test and a negative one. In the event that a requirement has sub-requirements, then each of the sub requirements also must at least two test cases, likewise composed of positive and negative.

10. What are the Unit tests written during the development cycle?

The tests are written before the code at the time of development in order to assist coders to create the best possible version.

11. Why not just use the clause System.out.printIn () for Testing?

Debugging of the code using system.out.printIn() just leads to a manual scanning of the entire output each time the program is run to make sure the code is performing operations as expected. However, the JUnit testing processes are much more effective and less probable for human error.

12. How do you Install JUnit?

• Download the latest version of the framework which is referred to as junit.zip
• Unzip the junit.zip compressed file to a directory known as %JUNIT_HOME%.
• Add JUnit to the classpath. Set the CLASSPATH to be %CLASSPATH%;%JUNIT_HOME%junit.jar
• Create a test on the installation by running the sample tests distributed with JUnit (sample tests are located within the installation directory-- not the junit.jar file). Then type java org. junit. Runner. JUnitCore org.junit.tests.AllTests
• Each one of the tests should then pass with an ‘Ok’ message. If the tests do not pass, then you will need to verify if junit.jar is within the CLASSPATH.

13. Is it a requirement to write the test case for each logic?

It is not necessary to write the test case for cases other than logic which can be reasonably broken.

14. Which are the most useful Junit extensions?

• XMLUnit
• Cactus
• Mock object
• JWebUnit

15. How is the testing of the protected method done?

To test the protected method, the test class must declared inside of a similar package as the target class.

16. How is the testing of the ‘private’ method done?

There is no direct means for testing the private method. Manual testing must be done, or else the method would be altered to the ‘protected’ method.

17. Why does JUnit only report the first failure during a single test?

The reporting of multiple failures within a single test would mean that a test is too large or attempting to test too many things at one time. Junit is created so that it works best within a small number of tests. It implements each of the tests within a separate instance of the testing class, giving a detailed report of the failure of each set test.

18. In Java, assert is a keyword. Will this likely contradict Junit’s Assert () Method?

Junit 3.7 deprecated assert () and replaced it with assert True(), which functions in the same manner. Junit 4 is compatible with the assert keyword. If you run with the –ea JVM switch, the failed assertions will be reported by Junit.

19. What are the parameterized tests in Junit?

In Junit 4, a new feature is named the ‘parameterized tests.’ These tests allow the developer to run the same test repeated for a number of different input values. The creation of parameterized tests with the use of Junit 4 is easy and includes the following steps:

• Annotate the Junit test class using @RunWith (Parameterized. Class). • Create a public static method and annotate with @Parameters which return a collection of object array to be used as the test dataset organized according to rows and columns.
• Create a public constructor, which would accept one row equivalent of the test information as the parameter.
• Create an instance variable for each of the fields or columns of row test data
• Create the test cases with the use of instance variables (columns) as the input test information.
• In each of the rows of the test data, the test cases may be executed after being invoked.

20. When is unit test garbage collected within Junit?

According to the design, the test instances are constructed during the first pass and the test execution is done during the second pass.The test runner holds strong references to each of the test instances for the duration of test implementation. For example, in the event of a long test run that has many of the test instances, none of the tests could have garbage collected until the time of the completion of the entire test run. It is necessary to program and free up resources, which are given or allowed in order to run a test. The explicit setting of the object to null within the teardown () method allows it to be garbage-collected before the end of the test run.

21. Which are the different approaches to approaching exceptions within Junit?

Approaches include the following:

• Try catch Idiom
• @Test annotation
• The use of Junit rule
• Use of catch exception library
• The use of customs annotation

22. 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.

23. When are the Junit unit tests written in the development cycle?

The unit tests are written before the development of the application. This is the case because writing the check before coding can assist the coders to write error-free codes that then boost the viability of the form.

24. Discuss and list the variety of Junit classes.

There are several essential classes used in both the testing and writing writing processes of JUnits. The list of the significant test classes include:

• Test Suite; this is a composition of different tests.
• Test Result; this is linked with the collection of results during the execution of a test case.
• Test Case; it is that sort of Junit class that is linked to different fixtures. There is the chance to run on a variety of tests as well.
• Assert; this is a set of assertive procedures which are utilized to design an application.

25. What are some of the main features of Junit?

The Junit test framework is linked with the provision of these significant features. They include the following:

• Junit classes
• Test Suites
• Fixtures
• Test Runners

26. Define installation in the context of Junit.

A fixture is a constant state of collection of objects, which are used for text implementation. The main objective of the use of a test fixture is in that there ought to be both familiar and fixed type of environment. At the same time, these tests are run so the results can be repeated. The features of these tests include some of the following:

• The setup method that runs every test • The teardown procedure that runs after the execution of each one of the tests

27. Give an account of the test suite when it comes to Junit.

The test suite refers to the principle of compiling a number of unit test cases in order to run it in a concurrent manner. It is important to note that when it comes to Junit, both Run With and The Suite comments are utilized in order to reveal the maximum advantages.

28. What is a fixture?

The fixture refers to a fixed state of a set of objects, which are used as the baseline for the running of tests. The objective of the test fixture is to make certain there is both a known and fixed environment where the tests are run so that the results can be repeated. It follows some of the following methods.

• Setup() method that runs before each test invocation • Teardown () method that runs after each test method.

29. What is a test runner?

The test runner is utilized for the execution of the test cases.

30. What are annotations and what are their uses within Junit?

Annotations resemble meta-tags, making it possible to add to your code and apply it to the methods or within class. The annotation in Junit allows information concerning test methods to be easily stored in plain text for ease-of-interface.

31. How is it possible to run Junit from command window?

• You first set the CLASSPATH
• Then, invoke the runner, such as java org.junit.runner. JUnitCore

32. What are the steps that are entailed in writing a simple Junit test case?

• The creation of a subclass of TestCase
• For the initializing the object under test, override the setup () method.
• The release the object under test, override the teardown () method
• Finally, set up one or more public testMethodname () methods which would evaluate the objects under the test and asset the results as expected.

33. What is the @ignore test annotation when it comes to the Junit framework?

When the Junit test code is not complete, it may fail to be implemented and then it can be annotated with the use of the @ignore annotation in order to prevent the test method/ class from being executed.

• When @Ignore is applied to the test method, it can prevent the method from being executed while the other methods within the class are executed.
• When @Ignore is applied to the test class, none of the test methods within the test class will be executed.
@Ignore would also take an optional default parameter if the user would like to mention or log why the test is being ignored in the first place.

34. How do you implement tests from the command line?

Run java org.junit.runner.JUnitCoreTestClass1 TestClass2, and so forth. For one shot type of test runs, users can utilize the static approach to runClasses (Class []). In the event that you want to add special listeners, create an instance of JUnitCore first and then use it for running the tests. You may also add a listener to be noted as the tests run.

35. How do you run Junit test cases within eclipse?

• Run each of the tests within the test class utilizing Alt+Shift+X, T or right click “Run As” to be greater than the Junit test.
• Go to the Junit view and expand on the tests which have already run.
• Right click on the desired test method and then click Run.

36. Give a comprehensive analysis of Joint Test API methods.

The following represents a list of implementation procedures that would assist in analyzing the issue:

• During the first step, users must utilize the annotation using the form of @before class.
• Make certain that you utilize the annotation @after class.
• Before the execution of the test class, you can ensure that you use @before performs.
• Use @before so application development process is smooth and hassle-free.

37. What is Mockito Junit?

Mockito is a mocking framework. It is based on JAVA as a library used for effective unit testing for JAVA applications. It is utilized to mock interfaces so a dummy functionality may be added to a mock interface, which may be utilized within unit testing.

38. What is PowerMock in Junit?

PowerMock is an open-source mocking library for the Java universe. It extends the present mocking frameworks like Mockito and EasyMock in order to make them stronger.

39. How do you debug a Junit test?

In the event of a test failure, the following debugging steps should be taken:

• Double-click on the entry from the Failure tab within the Junit view to open the corresponding file within the editor.
• Set a breakpoint at the start of the test method.
• Select the test case and execute Debug As>Junit Test from the Debug drop down.

40. What are some of the tools with which Junit can be easily integrated?

It can be integrated with some of the following:

• Ant
• Maven
• Eclipse

41. How do you test things that have to be run within the J2EE container such as servlets and EJBs?

Refactor the J2EE components in order to delegate on the functionality to other objects, which can be run outside of J2EE. This will drastically improve the testability and design of the software. Cactus is one of the open source Junit extensions which can be utilized for unit testing server-side java code.

42. What is the use of org.junit.JUnitCore class?

The test cases are executed with the use of JUnitCore class. JunitCore is a fallacy for running tests. It supports running Junit 4 tests, Junit 3.8.x, and mixtures.

43. How does one simulate a timeout situation within Junit?

Junit gives a handy option of Timeout. In the event that a test case takes a bit more time compared longer than a set number of milliseconds, then Junit will mark it as a failed exercise. This timeout parameter is used along with the @test annotation.

44. How is it possible to use Junit to test the code throw’s desired exception?

Junit gives users an option to trace the exception handling for the code. It is possible to test if the code throws desired exception or if it does not. The expected parameter is utilized along with @Test annotation in a manner like @Test(expected)

45. What happens in the event that a Junit test method is declared to be private?

In the case where a Junit test method is declared to be private, the program then compiles it in a successful manner. Though the execution is not going to succeed, Junit requires the test methods to be declared as ‘public’.

46. What occurs in the event that a Junit test method is declared to return ‘String’?

If the Junit test method is declared to return ‘String’, then the compilation is going to pass. However, the execution is still going to fail. That is because the Junit requires that the test methods would be declared to return ‘void’.

47. What is a mock object?

When it comes to unit tests, mock objects are able to simulate the behavior of the real objects, making them very useful when the real object is not a practical option or contained within this event, making it impossible to incorporate them into a unit test.

48. Explain the course of unit testing with the use of Mock objects.

The common coding style for testing when it comes to mock objects is:

• The creation of instances of mock objects
• Setting of a state and particular expectations within the mock objects.
• Invoking of a domain code with the mock objects as the parameters.
• Verifying the consistency within the mock objects.

49. What is a JWebUnit and what are its advantages?

The WebUnit is also known as java-based testing framework for web applications. It wraps the existing testing frameworks in order to provide for efficient testing of the web applications and comes available with a unified simple interface for testing. In order to verify the correct nature of an application, JWebUnit provides a high-level Java API for testing a web application, along with a set of particular assertions. These can include navigation through links, forms, entries, and submissions. It also entails the validation of table contents and other normal business-related web application attributes. The easy navigation approaches equipped with ready-to-use assertions make test creation easier, especially compared to programs like Junit or HtmlUnit alone. In the event that switching from HtmlUnit to other plugins like selenium are necessary, there would not be a need for rewriting the tests.

50. What is XMLUnit?

XMLUnit is utilized as a single Junit extension class, XMLTestCase, and a set of supporting classes. The assertions of the supporting classes are made concerning the following conditions:

• The distinction between pieces of XML like through Diff and DetailedDiff classes.
• The validation of a piece of XML via the Validator class.
• The result of transforming a piece of XML with the use of XSLT through transform class.
• The evaluation of the XPath expression from the XML through classes, which implement the XPath engine interface.
• Individual nodes within a piece of XML, which are exposed through DOM through Node Test class.

51. What is @Test and when/where is it used?

The @test annotation can be used for marking a method as a test method. The result is compared with the expected output in order to see whether or not a test was successful.

52. What is @BeforeClass and @Before, and how are they used?

• The syntax of @Before is: public void myMethod()
• The method should be executed before each of the tests. These methods are used for the initialization before the performance of an actual test within a testing environment.
• Syntax of @BeforeClass: public static void myMethod (). The method would be executed before each of the tests. It only executes one time. This method also needs to be declared static. It is commonly employed in database connectivity tasks before the execution of any of the tests.

53. Is it possible to change the return type of JUnit test method from void to another? type?

Ideally, this should not be possible. All of the Junit test approaches must have void return type. If one changes, the return type then the test method would not be seen as the test method and would consequently be ignored during the test execution.

54. Is it possible to pass command line arguments to the test execution?

It is possible for you to pass command line arguments to the test execution. It requires the following command:

• -D JVM command-line options

55. Is it necessary to write a test class for each class which must be tested?

No, there is no particular need to write an independent test class for each class being tested. In the event that there is a small group of tests which share a common test fixture, then these tests can be moved to a new testing class. If there were two groups of tests that could be executed separately from one another, then it would be better to place them in separate test classes.

56. Do you need to write a main () method within the Junit test case class?

This is similarly not necessary. Since it is possible to call a Junit runner to run the test case class as the system command, the explicit main () for a Junit test case is not recommended. The junit.textui.TestRunner.run() approach takes the test class name as the argument. This would find all of the class means which have names that begin with test.

author: patrick algrim
About the author

Patrick Algrim is an experienced executive who has spent a number of years in Silicon Valley hiring and coaching some of the world’s most valuable technology teams. Patrick has been a source for Human Resources and career related insights for Forbes, Glassdoor, Entrepreneur, Recruiter.com, SparkHire, and many more.


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