How to Test Custom Exception Error Codes Using JUnit 4

How can I test the error code of a custom exception using JUnit 4?

@Test
public void shouldThrowCustomExceptionWithErrorCode() {
    CustomException exception = assertThrows(CustomException.class, () -> {
        // Code that triggers the exception here
    });
    assertEquals("Expected error code", exception.getErrorCode());
}

Testing custom exceptions in JUnit 4 involves creating a test method that triggers the exception and checks its error code. This approach ensures that your exception handling works as expected.

public class CustomException extends Exception {
    private final String errorCode;

    public CustomException(String message, String errorCode) {
        super(message);
        this.errorCode = errorCode;
    }

    public String getErrorCode() {
        return errorCode;
    }
}

Causes

• Custom exception may not be properly thrown when an error occurs.
• The error code could be incorrectly set in your custom exception class.

Solutions

• Use the `assertThrows` method to specifically check for the expected exception type.
• Verify that the error code in your custom exception matches the expected value.

Mistake: Not checking the exception type when using assertThrows.

Solution: Always specify the expected exception type in the assertThrows method.

Mistake: Assuming the error code is set correctly without validating it in tests.

Solution: Explicitly check the error code returned from the exception to ensure it's accurate.