How does Mockito handle checked exceptions differently from unchecked exceptions

Checked Exceptions

- Definition: Checked exceptions are exceptions that are checked at compile time. They must be either caught in a `try-catch` block or declared in the method signature using the `throws` keyword[3].
- Mockito Handling: Mockito allows throwing checked exceptions from a mock object only if the exception is declared in the method signature. If you attempt to throw a checked exception that is not declared, Mockito will throw a `MockitoException` with a message indicating that the checked exception is invalid for that method[1][2]. For example, if a method `void someMethod() throws IOException`, you can use Mockito to throw an `IOException` without issues.

Unchecked Exceptions

- Definition: Unchecked exceptions are exceptions that are not checked at compile time. They are typically runtime exceptions or errors that indicate programming errors[3].
- Mockito Handling: Mockito can easily handle unchecked exceptions without any restrictions. You can use `thenThrow()` or `doThrow()` to simulate unchecked exceptions like `RuntimeException` or `NullPointerException` without needing them to be declared in the method signature[1][2]. This makes it straightforward to test error handling for unexpected conditions.

Workarounds for Checked Exceptions

If you need to throw a checked exception that is not declared in the method signature, you can use Mockito's `doAnswer()` method. This method allows you to define custom behavior for a mock method, including throwing exceptions that are not declared in the method signature[4]. However, this approach requires more manual handling and is generally less straightforward than using `thenThrow()` or `doThrow()`.

In summary, Mockito's handling of checked exceptions is more restrictive because it adheres to Java's compile-time checks, while unchecked exceptions can be thrown freely, making them easier to use in tests.