Discovered in #2467101: Fix DialogTest outside apache/mod_php: don't send multiple Accept request headers.
In core/modules/simpletest/src/WebTestBase.php there are two "sister" functions that get and post AJAX requests, respectively.
One is called drupalGetAJAX() and the other is called drupalPostAjaxForm() which will cause any OCD person to light the world on fire. :P
The coding standards at https://www.drupal.org/node/608152#naming state:
If an acronym is used in a class or method name, make it CamelCase too (SampleXmlClass, not SampleXMLClass). [Note: this standard was adopted in March 2013, reversing the previous standard.]
So let's rename it drupalGetAjax() instead. AFAIK this should be a BC-compatible change.