A simple and practical guide to testing and mocking with JMockit. The full implementation of this tutorial can be found on the GitHub project. A blog on JMockit, an open source software licensed under the MIT License. It includes APIs for mocking, faking, and integration testing, and a. We’ll see step by step in very short tutorials that’ll help you start using jmockit. I’ll be trying to keep each one as crisp as possible. If you want.

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A test method can contain any number of expectation blocks, including none. As shown above, the Expectations Object If InputStream was mocked “normally”, the read byte[] method would always be mocked, regardless of the instance on which it is called. New cascaded instances are created with Injectable semantics, so as to not affect other instances of the same type that may exist during the test.

First the Expectation API. It is particularly useful with parameters of a complex type think a JPA Entitywhich may contain several items whose values need to be checked.

JMockit: A beginner’s guide for Unit Testing – Knoldus Blogs

When using complex APIs where functionality is distributed through many different tutkrial, it is not uncommon to see chained invocations of the form obj1. Nicely ExplainedThanks.

Tested takes care of setting up properly initialized objects to be tested, while Mocked applies mocking to a given type. Cascading is quite useful in scenarios where a mocked class contains static factory methods. Unknown March 7, at 5: Inside this block, simply write invocations to one or more mocked types in the order they are tutkrial to have occurred.

Use Cascading if there is a method chain to be tested. The API provides a mocking annotation, Injectablewhich will only mock one instance of the mocked type, leaving others unaffected. Note that the use of Injectable is indeed necessary here, since the class under test extends the mocked class, and the method called to exercise ConcatenatingInputStream is actually defined in the base Tutorila class. After studying so many Jmokit Tutorials I found this one very Nice among all and easy to understand.


The Database class contains only static methods and a private constructor; the find and persist methods should be obvious, so we won’t list them here. Finally, the results from exercising the tested code are compared with the expected results. Finally, it’s worth noting that, if necessary, cascaded instances can be replaced with non-mocked ones, with a different mocked instance, or not be returned at all; for that, record an expectation which assigns the result field with the desired tutirial to be returned, or with null if no such instance is desired.

Rohit November 17, at 1: Thanks for all the effort you have put in writing this. There’s a lot of JMockit stuff to write about.

Learn Jmockit Tutorial – How to use it with Code coverage

With this alternative mechanism, we can rewrite the test as follows. Mocking is typically used in the construction of isolated unit tests, where a unit under test is exercised in isolation from the implementation of other units it depends on.

Any non-negative integer value is valid for any of the invocation count constraints. Notice that the expectation itself is specified through an isolated invocation to the mocked method. How to mock constructors with parameters or those that take arguments?

The type of the mock field or parameter can be any kind of reference type: In this tutorial we examine the APIs available in the library, with the help of example tests using Java 8. Typically, we use it when a single matching invocation is expected to occur; if more than one such invocation occurs, however, the last one to occur overwrites the values captured by previous ones. The test above will only pass if the tested code here embedded in the test method itself, for brevity invokes getValue on the exact same instance on which the recording invocation was made.

The Invocation object received during replay will provide access to the invoked instance and the actual invocation arguments, along with other abilities.


The second mechanism lets us associate a given mock instance with a recorded constructor expectation, and then use this instance for recording expectations on instance methods which will match invocations on future instances created with a matching constructor invocation. The most used methods are invokesetField and the getField.

In principle, any JDK of version 1. Well this was the situation we faced.

The JMockit Testing Toolkit Tutorial

Both mechanisms require the recording of an expectation on a specific constructor invocation a ” new ” expression of the mocked class. The first mechanism involves simply using the new instance obtained from the recorded constructor expectation, when recording expectations on instance methods. Want to test private methods and mock inner classes, use Deencapsulation.

Suppose we need to ttorial code which works with multiple instances of a given class, some of which we want to mock. So, how can we test the “doBusinessOperationXyz” method without making any changes to the existing application code? The latter is a mammoth process in itself. The assignment to result should tuutorial right after the invocation that identifies the recorded expectation, inside an expectation block.

Such objects can be created with any amount of state in internal instance fields; they will keep that state when mocked. What happens when some other internal code calls the same method with some other value? Mocked types and instances Expectations The record-replay-verify model Instantiation and injection of tested classes Recording results for an expectation Flexible matching of argument values Using the “any” fields Using the “with” methods Specifying invocation count constraints Tuotrial verification Verification in order Full verification Delegates: Abhinandan March 1, at 8: For instructions on how to add the library to a Java project, see Running tests with JMockit.