How to use mock and verify methods of OCMock in objective-C ? Is there any good tutorial on OCMock is available on the internet?

My problem is I am getting an error:

OCMckObject[NSNumberFormatter]: expected method was not invoked:setAllowsFloats:YES
 
I have written following Code:

- (void) testReturnStringFromNumber
{
    id mockFormatter = [OCMockObject mockForClass:[NSNumberFormatter class]];
    StringNumber *testObject = [[StringNumber alloc] init];    

    [[mockFormatter expect] setAllowsFloats:YES];
    [testObject returnStringFromNumber:80.23456];
    [mockFormatter verify];
}

@implementation StringNumber

- (NSString *) returnStringFromNumber:(float)num
{
    NSNumberFormatter *formatter = [[NSNumberFormatter alloc] init];
    [formatter setAllowsFloats:YES];
  
    NSString *str= [formatter stringFromNumber:[NSNumber numberWithFloat:num]];
   
    [formatter release];
    return str;
}

@end