How to stub a call to a method with a reference argument? - objective-c

Question

Consider this:
+(NSDictionary *)getDictionaryFromData:(id)data {
#synchronized(self) {
NSError *error = nil;
NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:&error];
if (error) {
DLog(#"SERIALIZATION FAILED: %#", error.localizedDescription);
return nil;
}
DLog(#"SUCCESS: %#", dict);
return dict;
}
}
How do I mock getDictionaryFromData to get coverage if error is not nil? Is it possible or do I have to actually mock the JSONObjectWithData method?

Answer 1

For this answer I'm assuming you don't actually want to mock the getDictionaryFromData: method. I assume you want to test its implementation, how it deal with an error case.
You can stub that JSONObjectWithData:options:error: method and return an error in the pass by ref argument; somehow like this:
id serializerMock = [OCMock mockForClass:[NSJSONSerialization class]];
NSError *theError = /* create an error */
[[[serializerMock stub] andReturn:nil] JSONObjectWithData:data
options:NSJSONReadingAllowFragments error:[OCMArg setTo:theError]];
The trick here is obviously the setTo: method.

Answer 2

Here is what worked for me (OCMock 3):
id serializerMock = OCMClassMock(NSJSONSerialization.class);
NSError *theError = [[NSError alloc] initWithDomain:NSCocoaErrorDomain code:NSPropertyListWriteInvalidError userInfo:nil];
OCMStub(ClassMethod([serializerMock dataWithJSONObject:OCMOCK_ANY
options:0
error:[OCMArg setTo:theError]]));
Note: For the line [serializerMock dataWithJSONObject...] Xcode's code completion does not work.