single underscore defines a protected variable/ method whereas double underscore defines a private.
Private attributes on a module are not avaliable in side classes that are defined, but are in functions that are defined on the module.
Private attributes on a module are not avaliable in side classes that are defined, but are in functions that are defined on the module.
Mox object's mocked element can only be used once and using it twice in the same test function will cause error.
