Allow filling in the only rich-text area without a locator

actiontext/lib/action_text/system_test_helper.rb

@@ -24,7 +24,7 @@ module SystemTestHelper
     #   # <input id="trix_input_1" name="message[content]" type="hidden">
     #   # <trix-editor input="trix_input_1"></trix-editor>
     #   fill_in_rich_text_area "message[content]", with: "Hello <em>world!</em>"
-    def fill_in_rich_text_area(locator, with:)
+    def fill_in_rich_text_area(locator = nil, with:)
       find(:rich_text_area, locator).execute_script("this.editor.loadHTML(arguments[0])", with.to_s)
     end
   end
@@ -33,12 +33,16 @@ def fill_in_rich_text_area(locator, with:)
 Capybara.add_selector :rich_text_area do
   label "rich-text area"
   xpath do |locator|
-    input_located_by_name = XPath.anywhere(:input).where(XPath.attr(:name) == locator).attr(:id)
+    if locator.nil?
+      XPath.descendant(:"trix-editor")
+    else
+      input_located_by_name = XPath.anywhere(:input).where(XPath.attr(:name) == locator).attr(:id)
 
-    XPath.descendant(:"trix-editor").where \
-      XPath.attr(:id).equals(locator) |
-      XPath.attr(:placeholder).equals(locator) |
-      XPath.attr(:"aria-label").equals(locator) |
-      XPath.attr(:input).equals(input_located_by_name)
+      XPath.descendant(:"trix-editor").where \
+        XPath.attr(:id).equals(locator) |
+        XPath.attr(:placeholder).equals(locator) |
+        XPath.attr(:"aria-label").equals(locator) |
+        XPath.attr(:input).equals(input_located_by_name)
+    end
   end
 end

actiontext/test/system/system_test_helper_test.rb

@@ -30,4 +30,10 @@ class ActionText::SystemTestHelperTest < ApplicationSystemTestCase
     fill_in_rich_text_area "message[content]", with: "Hello world!"
     assert_selector :field, "message[content]", with: /Hello world!/, type: "hidden"
   end
+
+  test "filling in the first rich-text area" do
+    visit new_message_url
+    fill_in_rich_text_area with: "Hello world!"
+    assert_selector :field, "message[content]", with: /Hello world!/, type: "hidden"
+  end
 end