Fake is callable even if not declared callable

[quantoid]

When rendering templates in Django the template engine will use callable() to decide whether to call a variable to resolve a value. When testing using a Fake object this results in an exception:

RuntimeError: fake:StatusPage object cannot be called (maybe you want Fake.is_callable() ?)

This is because Fake.__call__ is declared even though the fake is not expected to be called, so callable(fake) is always True and the template engine will try to call it.

Took me a while to realise this and come up with a workaround, which is to make sure the fake is callable and just returns itself so the template engine resolves it to itself:

my_fake.expects_call().returns(my_fake)

I'm not sure this is a bug, but I think it's something worth highlighting in the documentation. The documentation doesn't seem to be searchable, but I had a skim through and couldn't find a reference to callable().

[quantoid]

This would be a good place to mention the callable() gotcha: https://fudge.readthedocs.io/en/latest/api/fudge.html#fudge.Fake.is_callable

[quantoid]

Related python docs: https://docs.python.org/3.7/library/functions.html?highlight=callable#callable

[jwhitlock]

If the object has an attribute do_not_call_in_templates, then Django doesn't try to call it:

https://github.com/django/django/blob/97e637a87fb45c4de970cca6cb783d93473c9d15/django/template/base.py#L851-L853

This path was added when Django converted User.is_authenticated from a method to a boolean. Maybe this can help make a callable Fake that Django doesn't call in templates.