Add unsubscribe links and headers for emails

https://3.basecamp.com/2914079/buckets/37331921/todos/9002504172

test/controllers/notifications/unsubscribes_controller_test.rb

@@ -0,0 +1,40 @@
+require "test_helper"
+
+class Notifications::UnsubscribesControllerTest < ActionDispatch::IntegrationTest
+  setup do
+    @user = users(:david)
+    @access_token = @user.generate_token_for(:unsubscribe)
+
+    sign_in_as @user
+  end
+
+  test "new" do
+    get new_notifications_unsubscribe_path(access_token: @access_token)
+    assert_response :success
+  end
+
+  test "new with bad token" do
+    get new_notifications_unsubscribe_path(access_token: "bad")
+    assert_redirected_to root_path
+  end
+
+  test "create" do
+    @user.reload.settings.bundle_email_every_few_hours!
+    assert_changes -> { @user.reload.settings.bundle_email_frequency }, to: "never" do
+      post notifications_unsubscribe_path(access_token: @access_token)
+      assert_redirected_to notifications_unsubscribe_path(access_token: @access_token)
+    end
+  end
+
+  test "create with bad token" do
+    assert_no_changes -> { @user.reload.settings.bundle_email_frequency } do
+      post notifications_unsubscribe_path(access_token: "bad")
+      assert_redirected_to root_path
+    end
+  end
+
+  test "show" do
+    get notifications_unsubscribe_path(access_token: @access_token)
+    assert_response :success
+  end
+end