From https://once.com/writebook

test/models/first_run_test.rb

@@ -0,0 +1,37 @@
+require "test_helper"
+
+class FirstRunTest < ActiveSupport::TestCase
+  setup do
+    Book.destroy_all
+    User.destroy_all
+    Account.destroy_all
+  end
+
+  test "creating makes first user an administrator" do
+    user = create_first_run_user
+    assert user.administrator?
+  end
+
+  test "creates an account" do
+    assert_changes -> { Account.count }, +1 do
+      create_first_run_user
+    end
+  end
+
+  test "creates a demo book" do
+    assert_changes -> { Book.count }, to: 1 do
+      create_first_run_user
+    end
+
+    book = Book.first
+
+    assert book.editable?(user: User.first)
+    assert book.cover.attached?
+    assert book.leaves.any?
+  end
+
+  private
+    def create_first_run_user
+      FirstRun.create!({ name: "User", email_address: "user@example.com", password: "secret123456" })
+    end
+end