On May 31, 2007, at 3:46 PM, Mike R. Manzano wrote:
One example is the use of factory and abstract factory patterns for
decoupling. In a dynamic language, it can be a code smell since
the classes themselves can be treated like factories.
[…]
Your regular code can just ask Something for its defaultSomething.
For your test, you can write a subclass:
@interface SomethingForTesting : NSObject
+ (id)defaultSomething; // returns a different singleton than its
superclass
@end
Then just use that subclass in your test code instead of its
parent. Everything else will still use the parent class, but your
test code will use the subclass.
Yes, but it's not my test accessing the factory, it's the code that
it's testing. I shouldn't be altering that code to use the
SomethingForTesting subclass. The idea was to, in the test, have my
mock factory poseAs the real factory, so that in the code being
tested, the singleton that it ends up using is a mock object. Am I
missing something here?
@implementation ThingToTest
- (void) methodToTest
{
// It is here, in the method being tested, that a singleton is accessed
id aSingleton = [SingletonClass defaultSomething] ;
[aSingleton useThisSingleton] ;
}
@end
@interface MockSingletonClass : SingletonClass
+ (id) defaultSomething ; // override the real singleton's accessor
@end
@implementation MockSingletonClass
[…]
@end
// The test class
@interface TestThingToTest : SenTestCase
@end
@implementation TestThingToTest
- (void) testThingToTest
{
ThingToTest *thing = [[[ThingToTest alloc]init]autorelease];
[[MockSingletonClass class] poseAs:[SingletonClass]];
[thing methodToTest] ; // methodToTest uses the mock singleton ctor
// Here's where it would be nice to unposeAs.
}
@end
</codebarf>
On a separate note, that's good info regarding using the class itself
as a factory (I do that all the time--really convenient, and my
sample code above uses this pattern). However, in the real code, I
don't have a class, as the "root" of the hierarchy is a protocol, not
a class. Can protocols have static methods? That would be neat too.
