Extract #all_emoji? to a Rails ext

test/lib/rails_ext/string_test.rb

@@ -0,0 +1,11 @@
+require "test_helper"
+
+class StringTest < ActiveSupport::TestCase
+  test "#all_emoji?" do
+    assert "😊".all_emoji?
+    assert "😊😊😊".all_emoji?
+
+    assert_not "Hello 😊".all_emoji?
+    assert_not "Hello".all_emoji?
+  end
+end