Question

I am setting up unit tests to run methods that should generate an NSError. For some reason, I can’t get to the NSError from the unit tests. I created a sample method to test this, and it still doesn’t work. What am I doing wrong?

Implementation file:

- (BOOL)createAnError:(NSError **)error {
    NSMutableDictionary *errorDetail = [NSMutableDictionary dictionary];
    [errorDetail setValue:NSLocalizedString(@"This error should be testable", @"")
                   forKey:NSLocalizedDescriptionKey];
    [errorDetail setObject:self
                    forKey:NSValidationObjectErrorKey];
    NSError *cannotDeleteError = [NSError errorWithDomain:@"myErrorDomain" 
                                                     code:12345 
                                                 userInfo:errorDetail];
    if (*error = nil)
        *error = cannotDeleteError;

    return NO;
}

Unit Test:

- (void)testNSErrors {
    Unit *myObj = [NSEntityDescription insertNewObjectForEntityForName:@"TestObject" 
                                                  inManagedObjectContext:managedObjectContext];
    NSError *error = nil;
    STAssertFalse([myObj createAnError:&error], @"This method should return NO");
    STAssertEquals([error code], 12345, @"The error code is incorrect. (error = %@)", error);
}

The error I’m seeing in the build results is: error: -[LogicTests testNSErrors] : '0' should be equal to '12345': The error code is incorrect. (error = (null)).

So why is this happening? Am I creating the NSError incorrectly, testing for it incorrectly, or both?

Thank you!

Answer 1

You are not creating the error correctly. In your sample method, you test for if (*error = nil). This is an assignment. What you really mean to say is: if (*error == nil), which uses the equality operator.

Change that and you should get a positive result.