When should I use Mockito's doAnswer versus thenReturn?

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#1

I’m using Mockito for service layer unit testing and I’m trying to understand the differences between doAnswer and thenReturn. When should I use doAnswer versus thenReturn? I’ve primarily used thenReturn so far, but I’m unsure when doAnswer might be more appropriate. Can someone explain the details of using mockito doanswer?

#2

Hey Shreshthaseth,

Returning Values from a Mock thenReturn: Use thenReturn when you need to specify a fixed return value for a method call. It’s straightforward and ideal for simple cases where the method being mocked should return a specific value.

when(mock.someMethod()).thenReturn(“fixed value”); Example: If you have a method getUserName that should always return “John Doe”, use thenReturn:

when(mock.getUserName()).thenReturn(“John Doe”);

#3

Hey Shreshthaseth,

Handling Multiple Calls with Different Results : thenReturn: You can use thenReturn with multiple arguments to return different values on successive calls. This is useful when you want to simulate varying responses.

when(mock.someMethod()).thenReturn(“first value”, “second value”, “third value”);

doAnswer: Use doAnswer when you need to execute custom logic or return different values based on the input or call context. It provides more flexibility than thenReturn. doAnswer(invocation → { Object[] args = invocation.getArguments(); return "value based on " + args[0]; }).when(mock).someMethod(anyString());

Example: If getUserRole should return different roles based on the input, you can use doAnswer:

doAnswer(invocation → { String role = (String) invocation.getArguments()[0]; return "Role for " + role; }).when(mock).getUserRole(anyString());

#4

Hello @Shreshthaseth and everyone!

When dealing with complex behavior in mocking, the doAnswer method is your go-to tool. It’s particularly useful when you need to perform intricate actions during method calls, like modifying arguments, invoking real methods, or interacting with other mocks.

Here’s a basic structure for using doAnswer:

java

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doAnswer(invocation -> {
    // Complex behavior or side effects
    return someComplexResult;
}).when(mock).someMethod();

Example: Let’s say you have a method updateDatabase that needs to perform logging and return a result based on complex conditions. doAnswer is perfect for this scenario:

java

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doAnswer(invocation -> {
    Object[] args = invocation.getArguments();
    System.out.println("Updating database with " + args[0]);
    // Perform actual update
    return true;  // Return result
}).when(mock).updateDatabase(any());

In summary, if you need straightforward fixed returns or simple sequences of values, use thenReturn. However, when you want to customize behavior, handle varying inputs, or execute complex actions during method calls, opt for doAnswer.

Happy coding! If you have any questions or need further clarification, feel free to ask!