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

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JUnit or often referred to as just "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 to ensure web and native applications meet certain user story criteria in an automated fashion. If you can think about the process of clicking around a website or application and thinking through the variations that might exist in order to produce a certain feature, it would be quite time-consuming. Unit testing helps to mock out certain scenarios which can then be automated. 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. And gives the developer the ability to back through the work and figure out why that parcitular feature didn't work as a baseline or why it didn't work when potentially merged into multiple team members work. This process often happens before heavy software releases but is becoming more commong to do on a regular basis as software applications are becoming more and more robust. Below are some common junit interview questions and answers 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 what your particular way of describing that answer is. It will convey more confidence and help you in the long run.

1. What is Junit?

This is a testing type of framework used for Java Programming Languages. It is written in Java and has been crucial in the development of test-driven development. It is one of a range of unit testing frameworks that are collectively referred to as xUnit, which came from SUnit. It was developed by Erich Gamma and Kent Beck. It assists the developer to write and execute repeatable automated tests. It is an application-programming interface for the development of test cases within java that is part of the XUnit family. Junit has also been ported to a number of other languages including PHP, Python and even C++.

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

Junit gives a particular development framework, which allows for the following to occur;

• Testing early and allows for automated testing
• The framework allow for testing code reusage.
• The Junit tests may be integrated with the build meaning the 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?

Testing refers to the ways of checking on the functionality nature of the application concerning whether it lives up to the stated requirements or does not.

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

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

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

• It is time consuming and tedious- because the test cases are done by people, it is also prone to errors and is time consuming.
• There is a big investment given to human resources. So as the test cases need to be executed manually, more testers are needed when it comes to manual testing.
• It is non-programmable- there is no real programming which can be done in order to write the sophisticated tests that fetch hidden information.
• It is not very reliable: manual testing is less reliable because the tests may not be done with precision, each instance due to the occurrence of errors.

6. What are the inherent advantages of Automated Testing?

• It is quite fast as automation runs test cases in a significant manner faster than the human resources do.
• There is a lesser investment, which is given to human resources because the test cases are executed using automation tools. That means less testers are needed within automation testing.
• They are programmable as the testers are able to program sophisticated tests in order to display hidden information.
• More reliable: the automation tests perform the same thing every time they run in a way that a person would not be able to.

7. What are the significant features of a Junit?

• It provides an open source framework.
• It gives the test runners that in turn run the tests.
• It gives assertions concerning the testing for expected results.
• The JUnit tests may be run automatically and they check their results and allow for immediate feedback.
• The JUnit tests may be organized according to test suites, which have test cases, and other suites.
• The JUnit reveals test progress within a bar that is green if the test is going the right way and red when 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 would be expected. In order for one to achieve these results in a quick fashion, the test framework is needed. JUnit presents as a 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 by a known input and by 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. That would be one positive test and a negative one. In the event that a requirement has sub requirements then each of the sub requirements have to have at least two test cases as the positive and the negative.

10. What are the Unite tests written within the development cycle?

The tests are written before the code at the time of development in order to assist the 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 in order to make certain the code is doing the operations as expected. The other thing is in the end, it takes a lesser amount of time to code Junit methods and test them within the class files.

12. How to 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 through running of the sample tests distributed with JUnit (sample tests are located within the installation directory and not the junit.jar file). The type java org. junit. Runner. JUnitCore org.junit.tests.AllTests
• Each one of the tests would 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 a necessary requirement to write the test case only for that 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 would have to be declared within 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 so manual testing is to be done or 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 refers to a sign the test does too much and it is too big on a unit test. Junit is created so that it works best within a number of small tests. It implements each of the tests within a separate instance of the testing class. It gives a report of the failure on each set test.

18. In Java, assert is a keyword. Is this going to contradict Junit’s Assert () Method?

Junit 3.7 deprecated assert () and replaced it with assert True(), that works in the same manner. Junit 4 is compatible with the assert keyword. If you run with the –ea JVM switch, the assertions, which fail, are going to be reported by Junit.

19. What are the parameterized tests in Junit?

In Junit 4, a new feature is named the ‘parameterized tests’, are brought in that 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 the steps include the following.

• Annotating 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 are the unit tests 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 time of the second pass. The test runner holds strong references to each of the test instances for the duration of the test implementation. For example, in the event of a long test run that has many of the Test instances none of the tests could be garbage collected up to the time of the completion of the entire test run. There is a need 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 of exception handling within Junit?

They include the following:

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

22. Define Junit according to the current context of evolving technologies.

Junit is known as a waning testing framework. It is extensively utilized by developers when carrying out; unit testing in Java. At the same time, it is also being used for speeding up the application based on Java. It is crucial to note that through considering the source code, the application would be efficiently sped up.

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

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

24. Discuss the variety of Junit classes and make a list of them.

These are some of the essential classes, which are utilized in testing, and writing of the 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 main fixtures within 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 when it comes to Junit.

A fixture is also referred to as a constant state of collection of objects, which would then be used for the text implementation. The main objective of the use of a test fixture is in the fact there ought to be a familiar and fixed type of environment. At the same time, these tests are run so the results can be repeated. That would comprise some of the following.

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

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

The test suite refers to the principle, which concerns compiling a number of unit test cases in order to run it in a concurrent manner. In this manner, it would be interesting 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 a known and fixed environment where the tests are run so 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 is their use within Junit?

Annotations resemble meta-tags in that it is possible to add to your code and apply them to the methods or within class. The annotation in Junit allows information concerning test methods, the methods that are going to run before and after the test methods and the methods run before and after all, of the methods, or the class of methods that will be ignored during execution.

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

• You first set the CLASSPATH
• Invoke the runner where it would be java org.junit.runner. JUnitCore

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

• Creation of a subclass of TestCase
• For initializing the object under test, override the setup () method.
• To release the object under test, override the teardown () method
• Set up one or more public testMethodname () methods which would evaluate the objects under 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 the @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 then none of the test methods within the test class would be executed.
@Ignore would take an optional default parameter if you would like to mention or log why the test is being ignored in the first place.

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

Run java org.junit.runner.JUnitCoreTestClass1 TestClass2 and so forth. For one shot type of test runs, you 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 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 ran.
• 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, there is a need to 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 proceed to make certain that you use @before performs.
• Use @before such that the application development process turns out to be 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 add stronger features to them.

39. How do you debug a Junit test?

In the event of a test failure, you can go along some of the following steps in order to debug it:

• Double click on the failure 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?

Refactoring of the J2EE components in order to delegate on the functionality to the other objects, which do not have to be run within a J2EE, is going to improve on the testability and the design of the software. Cactus is one of the open source Junit extensions, which would 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 as compared to a particular number of milliseconds then Junit is going to 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 throws desired exception?

Junit gives an option of tracing 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 then it compiles in a successful manner. Though the execution is not going to succeed. The reason is that 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 okay. Though, the execution is still going to fail. That is because the Junit would require 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 and so they are very useful when the real object is not a practical option or in the event, that it is not possible 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
• Set a state and particular expectations within the mock objects.
• Invoke domain code with the mock objects as the parameters.
• Verify the consistency within the mock objects.

49. What is a JWebUnit and what are the 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 gives a high level Java API in for testing a web application along with a set of particular assertions. That would include navigation through links and forms entry and submission. It also entails the validation of table contents and other normal business web application attributes. The easy navigation approaches which come with ready to use assertions make it better for better test creation as opposed to using Junit or HtmlUnit only. In the event that switching from HtmlUnit to other plugins like selenium are needed, there would not be a need for rewriting the tests.

50. What is XMLUnit?

What are the uses of the supporting classes within 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.

• 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 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 if the test was successful or if it was not.

52. What is @BeforeClass and @Before and how is it used?

• The syntax of @Before is : public void myMethod()
• The method should execute 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. The method needs to be declared static. It is used a lot of the time for 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 the case. All of the Junit test approaches need to have a void return type. If one changes, the return type then the test method would not be seen as the test method and it would 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 would have to be the following command

• -D JVM command-line options

55. Is there a need to write a test class for each class, which needs to be tested?

No there is not a particular need to write an independent test class for each class that needs to be tested. In the event there is a small group of tests, which share a common test fixture, then you can move these tests to a new testing class. If there were two groups of tests that you think you would execute 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?

It is not necessary. Though developers write the main () method within the Junit test case class in order to call a Junit test runner to run the tests which are defined in the class. 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.

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