From https://once.com/writebook

test/system/edit_page_test.rb

@@ -0,0 +1,19 @@
+require "application_system_test_case"
+
+class EditPageTest < ApplicationSystemTestCase
+  setup do
+    sign_in "kevin@37signals.com"
+  end
+
+  test "edit page" do
+    visit edit_book_page_url(books(:handbook), leaves(:welcome_page))
+    assert_selector "house-md"
+
+    fill_house_editor "page[body]", with: "Welcome to the handbook! This is the **first** page."
+
+    click_button "Save"
+
+    assert_selector ".house-md-content", text: "Welcome to the handbook! This is the **first** page."
+    assert_selector ".house-md-content strong", text: "first"
+  end
+end