module GeneratorSpec::GeneratorExampleGroup::InstanceMethods

end
end
assert_match /Product\.all/, index
assert_instance_method :index, content do |index|
assert_file "app/controller/products_controller.rb" do |controller|

it yields the content of the method.
Asserts the given method exists in the given content. When a block is given,

def assert_instance_method(method, content)
  assert content =~ /def #{method}(\(.+\))?(.*?)\n  end/m, "Expected to have method #{method}"
  yield $2.strip if block_given?
end