I’m reading an ebook version, therefore only the section number instead of a page number. It’s part of the “Easy integration testing with nested modules” section.

The advanced_code_gen/translator_test.exs file contains an integration test that states:

test " it allows multiple locales to be registered" do
  assert I18n.t("fr", "flash.notice.hello", first: "Jaclyn", last: "M") == "salut Jaclyn M!"
end

But what actually gets tested in this function is the interpolation binding and thereby is equal to the next integration test:

test "it interpolates bindings" do
  assert I18n.t("en" "flash.notice.hello", first: "Hason", last: "S") ==  "hello Jason S!"
end

Since two different languages are used, the combination is kind of testing the multiple locales, but it’s bad practice to do it in this way.