Example of how you could compare two classes to make sure their interfaces match

example_of_how_to_compare_two_classes_to_make_sure_their_interfaces_match.rb

class LHS
  def correct()             end
  def wrong_num_args(a)     end
  def wrong_arg_types(a,b:) end
  def wrong_name(a)         end
  def lhs_only()            end
end

class RHS
  def correct()             end
  def wrong_num_args(a, b)  end
  def wrong_arg_types(a, b) end
  def wrong_name(b)         end
  def rhs_only()            end
end

def compare_interfaces(lhs, rhs)
  methods = lhs.instance_methods(false) | rhs.instance_methods(false)
  methods.map do |name|
    lhsm = (lhs.instance_method(name) rescue nil)
    rhsm = (rhs.instance_method(name) rescue nil)
    [name, lhsm&.parameters, rhsm&.parameters]
  end
end

def pretty_params(parameters)
  return "missing" unless parameters
  pretty_params = parameters.map do |type, name|
    case type
    when :req     then name
    when :opt     then "#{name}=..."
    when :rest    then "*#{name}"
    when :keyreq  then "#{name}:"
    when :key     then "#{name}:..."
    when :keyrest then "**#{name}"
    when :block   then "&#{name}"
    else raise "huh? #{type.inspect}"
    end
  end
  "(#{pretty_params.join ', '})"
end

def assert_interfaces!(lhs, rhs)
  desc = compare_interfaces(lhs, rhs)
           .reject { |_, l, r| l == r }
           .map { |name, l, r| <<~MSG.gsub /^/, "  " }
             ##{name}
               #{lhs}: #{pretty_params l}
               #{rhs}: #{pretty_params r}
           MSG
           .join("\n")
  raise TypeError, "Interface mismatch:\n#{desc}", caller
end

assert_interfaces! LHS, RHS # ~> TypeError: Interface mismatch:\n  #wrong_num_args\n    LHS: (a)\n    RHS: (a, b)\n\n  #wrong_arg_types\n    LHS: (a, b:)\n    RHS: (a, b)\n\n  #wrong_name\n    LHS: (a)\n    RHS: (b)\n\n  #lhs_only\n    LHS: ()\n    RHS: missing\n\n  #rhs_only\n    LHS: missing\n    RHS: ()\n

# ~> TypeError
# ~> Interface mismatch:
# ~>   #wrong_num_args
# ~>     LHS: (a)
# ~>     RHS: (a, b)
# ~> 
# ~>   #wrong_arg_types
# ~>     LHS: (a, b:)
# ~>     RHS: (a, b)
# ~> 
# ~>   #wrong_name
# ~>     LHS: (a)
# ~>     RHS: (b)
# ~> 
# ~>   #lhs_only
# ~>     LHS: ()
# ~>     RHS: missing
# ~> 
# ~>   #rhs_only
# ~>     LHS: missing
# ~>     RHS: ()
# ~>
# ~> /var/folders/7g/mbft22555w3_2nqs_h1kbglw0000gn/T/seeing_is_believing_temp_dir20180606-89092-tr75on/program.rb:55:in `<main>'