How do I ensure that each thenThrow() call is executed only once

Understanding Mockito's Stubbing

Mockito allows you to stub methods so that they behave in a specific way during testing. For methods that return void, you typically use `doThrow()` instead of `thenThrow()`, as `thenThrow()` is used for methods that return a value.

Using `doThrow()` for Void Methods

When you want a void method to throw an exception only once, you can chain multiple `doThrow()` calls with `doNothing()` to specify the behavior for subsequent calls. Here's how you can do it:

java
// First call throws an exception
doThrow(new RuntimeException()).doNothing().when(mockedObject).voidMethod();

In this example, the first call to `voidMethod()` will throw a `RuntimeException`, and subsequent calls will do nothing.

Handling Multiple Calls with Different Behaviors

If you need to throw exceptions on specific calls (e.g., first and third calls), you can chain multiple `doThrow()` and `doNothing()` calls accordingly:

java
// First call throws, second does nothing, third throws, fourth does nothing
doThrow(new RuntimeException()).doNothing().doThrow(new RuntimeException()).doNothing().when(mockedObject).voidMethod();

This setup ensures that only the first and third calls to `voidMethod()` throw exceptions.

Using `doAnswer()` for More Complex Logic

For more complex scenarios where you need to dynamically decide whether to throw an exception based on some condition (like the number of calls), you can use `doAnswer()` with an `Answer` object:

java
int callCount = 0;
doAnswer(invocation -> {
    callCount++;
    if (callCount == 1 || callCount == 3) {
        throw new RuntimeException();
    }
    return null; // For void methods, return null
}).when(mockedObject).voidMethod();

This approach allows you to implement any logic you need to decide when to throw an exception.

Summary

- Use `doThrow()` for void methods to throw exceptions.
- Chain `doThrow()` and `doNothing()` calls to control the behavior of subsequent method calls.
- For complex logic, use `doAnswer()` with an `Answer` object to dynamically decide when to throw exceptions.