TypeError: superclass must be a Class (Module given)

I have a class which inherits another class

Class A
end

Class A::B < A
end

I am trying to write specs for class B by describing it as:

describe A::B, type: :class do
 #some test here
end

But i get this error: TypeError: superclass must be a Class (Module given) on spec file'd describe line. How can i fix this?