Test whether a Ruby class is a subclass of another class

Question

Just use the < operator

B < A # => true
A < A # => false

or use the <= operator

B <= A # => true
A <= A # => true

Also available:

B.ancestors.include? A

This differs slightly from the (shorter) answer of B < A because B is included in B.ancestors:

B.ancestors
#=> [B, A, Object, Kernel, BasicObject]

B < B
#=> false

B.ancestors.include? B
#=> true

Whether or not this is desirable depends on your use case.