CustomException with error code - junit

Question

I have created a CustomException with a custom message and an error code.
public class CustomException extends RuntimeException{
private int errorCode;
public CustomException(String message,int errorCode){
super(message);
this.errorCode=errorCode;
}
public int getErrorCode(){
return this.errorCode;
}
public String getMessage(){
return "Message: "+super.getMessage()+" ErrorCode: "+this.errorCode;
}
}
When I add a null value in a list throw CustomException with the message "Null" and error Code 1. When I add an empty value the message for exception is "Empty" and error Code 2.
How I can capture and test error code in unit test?
I have done something like that:
public class MyListTester{
private Class exceptionType = CustomException.class;
#Test
public void testAddNonNullValue() {
exception.expect(exceptionType);
exception.expectMessage("Null");
list.add(null);
}
but I don't have acces to the error code

Answer 1

The trick is to use the expect method of the ExpectedException rule which takes a Matcher as parameter and to write a custom matcher for verifying the error code. Here is a complete example:
public class MyListTester {
#Rule
public ExpectedException exception = ExpectedException.none();
#Test
public void testAddNullValue() {
MyList list = new MyList();
exception.expect(CustomException.class);
exception.expectMessage("Null");
exception.expect(errorCode(1));
list.add(null);
}
#Test
public void testAddEmptyValue() {
MyList list = new MyList();
exception.expect(CustomException.class);
exception.expectMessage("Empty");
exception.expect(errorCode(2));
list.add(emptyValue);
}
private Matcher<? extends CustomException> errorCode(final int errorCode) {
return new CustomTypeSafeMatcher<CustomException>("errorCode " + errorCode) {
#Override
protected boolean matchesSafely(CustomException e) {
return e.getErrorCode() == errorCode;
}
};
}
}