stub_strict.rb

require 'minitest/mock'

module StubStrict
  module_function

  def render_parameters(ruby_parameters)
    ruby_parameters.map { |type, name|
      case type
      when :req;     name.to_s
      when :opt;     "#{name} = 'value'"
      when :rest;    "*#{name}"
      when :key;     "#{name}: 'value'"
      when :keyreq;  "#{name}:"
      when :keyrest; "**#{name}"
      when :block;   "&#{name}"
      end
    }.join(', ')
  end

  def wrap_with_verifier(val, name, rendered_args)
    obj = Object.new
    eval "def obj.verify_args(#{rendered_args}); end",
      binding, __FILE__, __LINE__ - 1

    ->(*a, **k, &b) {
      begin
        obj.verify_args(*a, **k, &b)
      rescue ArgumentError
        raise ArgumentError,
          'Stubbed args are incompatible with the original method. ' \
          "Expected signature: #{name}(#{rendered_args})"
      end

      val.respond_to?(:call) ? val.call(*a, **k, &b) : val
    }
  end

  module ObjectExt
    def stub_strict(name, val, *, **, &)
      expected_args =
        if name == :new && method(:new).source_location.nil?
          instance_method(:initialize).parameters
        else
          method(name).parameters
        end

      rendered_args = StubStrict.render_parameters(expected_args)
      wrapped_args = StubStrict.wrap_with_verifier(val, name, rendered_args)
      stub(name, wrapped_args, *, **, &)
    end
  end
end

class Object
  include StubStrict::ObjectExt
end