Problem/Motivation
Step 2 of #2304461: KernelTestBaseTNG™
\Drupal\simpletest\KernelTestBase is marked as deprecated for removal before Drupal 8.2.x, which is right around the proverbial corner.
Proposed resolution
Create a single patch that has all the conversions. If that becomes problematic, split out those difficult tests to their own issue.
Remaining tasks
https://www.drupal.org/node/2489956 has some instructions on what to do during a conversion. For additional assistance, use #2678534: Convert editor.module's kernel tests to NG as an example of what things should look like.