Testing profile unable to show ajax confirmation messages

Problem/Motivation

While I was writing the tests of #2910738: Ajaxify the confirmation message, I found that the default testing profile is unable to render the confirmation message which are retuned as an ajax response. Right now, as a workaround, I am executing the tests using standard profile.

testing profile is recommended as it provides a very raw Drupal setup which is ideal for tests.

Proposed resolution

If we are going to use testing profile, maybe we need to add to a library or something in the test setUp(), the library will help to render ajax responses.

Remaining tasks

Not yet decided.

User interface changes

N/A

API changes

N/A

Data model changes

N/A