Rails项目,在使用capybara进行测试时:ArgumentError:传递给capybara::querys::SelectorQuery的未使用参数:[4]

测试表单是否有4个输入无效,我正在复制粘贴文档中的行:

assert_select "form input", 4

require "application_system_test_case"

class QuestionsTest < ApplicationSystemTestCase
  test "visiting /ask renders the form" do
    visit ask_url

    assert_selector "p", text: "Ask your coach anything"

    assert_select "form input", 4
  end
end

完整的错误消息是:

Error:
QuestionsTest#test_visiting_/ask_renders_the_form:
ArgumentError: Unused parameters passed to Capybara::Queries::SelectorQuery : [4]
    test/system/questions_test.rb:9:in `block in <class:QuestionsTest>'

任何帮助都将不胜感激。