Open Radar

 
The STAssertNil and STAssertNotNil macros are commonly used and very handy, but their output when an assertion fails leaves quite a bit to be desired. Here's an example of what such failures look like today:

- (void) testFAIL {
	id bar = nil;
	STAssertNil([NSObject new], nil);
	STAssertNil(@"foo", nil);
	STAssertNil(self, nil);
	STAssertNotNil(bar, nil);
}

The errors that result from this test read as follows (trimmed for space):

	error: -[SampleTest testFAIL] : "(([NSObject new]) == nil)" should be true. 
	error: -[SampleTest testFAIL] : "((@"foo") == nil)" should be true. 
	error: -[SampleTest testFAIL] : "((self) == nil)" should be true. 
	error: -[SampleTest testFAIL] : "((bar) != nil)" should be true. 

These errors would be more intelligible and self-evident if they read more like this:

	error: -[SampleTest testFAIL] : [NSObject new] should be nil. 
	error: -[SampleTest testFAIL] : @"foo" should be nil. 
	error: -[SampleTest testFAIL] : self should be nil. 
	error: -[SampleTest testFAIL] : bar should be non-nil. 

The current error messages are produced using +failureInCondition:isTrue:inFile:atLine:withDescription: (the same NSException class method used by STAssertTrue and STAssertFalse) and wrap the expression text such that it looks vaguely like Lisp.

Adding a new class method (+failureInExpression:isNil:inFile:atLine:withDescription:) to NSException and slightly modifying the STAssertNil and STAssertNotNil macros makes these tests much more intelligible with minimal effort. I've attached a sample implementation (based on the old Sen:te source, as in <rdar://problem/7670449>) which I've verified to work with my existing unit tests.

------------ attachment included below for this report --------------

// NSException_SenTestFailure.h, add to @interface NSException(SenTestFailure)

+ (NSException *) failureInExpression:(NSString *)expression
                                isNil:(BOOL)isNil
                               inFile:(NSString *)filename
                               atLine:(int) lineNumber
                      withDescription:(NSString *) formatString, ...;

// NSException_SenTestFailure.m, add to @implementation NSException(SenTestFailure)

+ (NSException *) failureInExpression:(NSString *)expression
                                isNil:(BOOL)isNil
                               inFile:(NSString *)filename
                               atLine:(int) lineNumber
                      withDescription:(NSString *) formatString, ...
{
    NSString *description;
    if (formatString != nil) {
        va_list argList;
        va_start(argList, formatString);
        description = [[[NSString alloc] initWithFormat:formatString 
                                              arguments:argList] autorelease];
        va_end(argList);
    } else {
        description = @"";
    }
    
    NSString *reason = [NSString stringWithFormat:@"%@ should be %@. %@",
                        expression, (isNil ? @"nil" : @"non-nil"), description];
    NSDictionary *userInfo = [NSDictionary dictionaryWithObjectsAndKeys:
                              SenConditionFailure, SenFailureTypeKey,
                              expression, SenTestConditionKey,
                              filename, SenTestFilenameKey,
                              [NSNumber numberWithInt:lineNumber], SenTestLineNumberKey,
                              description, SenTestDescriptionKey,
                              nil];
    return [self exceptionWithName:SenTestFailureException
                            reason:reason
                          userInfo:userInfo];

}

// SenTestCase_Macros.h, replace existing STAssertNil and STAssertNotNil macros

#define STAssertNil(a1, description, ...) \
do { \
    @try {\
        if ((a1) != nil) { \
            [self failWithException:([NSException failureInExpression:[NSString stringWithUTF8String:#a1] \
                                                                isNil:YES \
                                                               inFile:[NSString stringWithUTF8String:__FILE__] \
                                                               atLine:__LINE__ \
                                                      withDescription:@"%@", STComposeString(description, ##__VA_ARGS__)])]; \
        } \
    }\
    @catch (id anException) {\
        [self failWithException:([NSException failureInRaise:[NSString stringWithFormat:@"(%s) == nil fails", #a1] \
                                                   exception:anException \
                                                      inFile:[NSString stringWithUTF8String:__FILE__] \
                                                      atLine:__LINE__ \
                                             withDescription:@"%@", STComposeString(description, ##__VA_ARGS__)])]; \
    }\
} while(0)

#define STAssertNotNil(a1, description, ...) \
do { \
    @try {\
        if ((a1) == nil) { \
            [self failWithException:([NSException failureInExpression:[NSString stringWithUTF8String:#a1] \
                                                                isNil:NO \
                                                               inFile:[NSString stringWithUTF8String:__FILE__] \
                                                               atLine:__LINE__ \
                                                      withDescription:@"%@", STComposeString(description, ##__VA_ARGS__)])]; \
        } \
    }\
    @catch (id anException) {\
        [self failWithException:([NSException failureInRaise:[NSString stringWithFormat:@"(%s) != nil fails", #a1] \
                                                   exception:anException \
                                                      inFile:[NSString stringWithUTF8String:__FILE__] \
                                                      atLine:__LINE__ \
                                             withDescription:@"%@", STComposeString(description, ##__VA_ARGS__)])]; \
    }\
} while(0)