ProductCollectionViewModel Testing

Summary:
	-Tested:
		#loadWithErrorHandler
		#addProductViewModel:
		#removeProductViewModel:
		#productAtIndex:
		#productsCount
		#indexOfProductViewModel:
you should add a `beforeEach` and `afterEach` statements to set up common objects that will be commonly used.

```objc
__block ProductViewModel * productVM;
beforeEach(^{
    productVM = [[ProductViewModel alloc] initWithProduct:notAddedProduct andRepository:repository];
});
afterEach(^{
    productVM = nil;
});
```