How to Return an Argument to a Mocked Method in Mockito?

How to Make a Mocked Method Return an Argument Passed to It Using Mockito

Mockito is a Java mocking framework that allows the creation of mock objects for testing purposes. Mocking methods helps test code independently of its dependencies. In this scenario, we want to mock a method to return a value that was passed to it during the method call.

Solution:

Since Mockito version 1.9.5 and Java 8, lambda expressions can be utilized to achieve the desired functionality. Here's how:

<code class="java">when(myMock.myFunction(anyString())).thenAnswer(i -> i.getArguments()[0]);</code>

In this lambda expression, i represents an instance of InvocationOnMock and i.getArguments()[0] retrieves the first argument passed to the mocked method.

Alternative Solution for Older Versions:

For older versions of Mockito, an Answer can be implemented to achieve the same result. Here's an example:

<code class="java">when(mock.myFunction(anyString())).thenAnswer(new Answer<String>() {
    @Override
    public String answer(InvocationOnMock invocation) throws Throwable {
        Object[] args = invocation.getArguments();
        return (String) args[0];
    }
});</code>

In this Answer implementation, the arguments array is retrieved from the InvocationOnMock instance, and the first argument (string) is returned.

Using these methods, you can configure mocked methods in Mockito to return values based on the arguments passed to them, allowing for more flexible and realistic testing scenarios.

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