gistfile1.rb

#!/usr/bin/env ruby

class A
    def a; end
    def b; end
end

class B < A
    def a; end
end

class C < B; end
class D < A; end
class E < A;
    def b; end
end
    

ObjectSpace.each_object( Class ) do |klass|
    if klass < A
        inherited_methods = A.instance_methods(false) - klass.instance_methods(false)
        puts "#{klass} methods not overridden:", *inherited_methods
    end
end

# B methods not overridden:
# b
# C methods not overridden:
# a
# b
# D methods not overridden:
# a
# b
# E methods not overridden:
# a