如何在单个示例中使用多个RSpec上下文？

describe "MyApp" do
  # ...
end

describe "MyApp" do
  context "when user is logged in" do
    # ...
  end

  context "when user is not logged in" do
    # ...
  end
end

describe "MyApp" do
  context "when user is logged in" do
    it "displays the user's profile page" do
      # ...
    end

    it "allows the user to create a new post" do
      # ...
    end
  end

  context "when user is not logged in" do
    it "redirects to the login page" do
      # ...
    end

    it "displays a message to prompt user login" do
      # ...
    end
  end
end