Improve docblocks about migration source plugins testing (MigrateSqlSourceTestCase)

Looks pretty good, thanks!

Can you fix the paragraph wrapping?

+   * Database contents represents a mocked database. It should contain an
+   * associative array with the table name as key, and as many nested arrays as
+   * the number of rows we are mocking.
+   * Each of those faked rows must be another associative array with the column
+   * name as the key and the value as the cell.

If you want this as two paragraphs, put a blank line in between. If it is one, wrap it as one.

Also,

   const ORIGINAL_HIGHWATER = '';

This doesn't have docs?

And

+  /**
+   * Expected results of the source parsing.
+   * @var array
+   */
   protected $expectedResults = array();

Needs a blank line before the @var.

Great!

I need someone else to verify this change:

-   * @var \Drupal\migrate\Plugin\migrate\source\d6\Comment.
+   * @var \Drupal\migrate\Plugin\migrate\source\d6\Drupal6SqlBase.
    */
   protected $source;

No idea if that is correct or not.

Everything else looks OK. Some of the wording is slightly awkward, but it's clear enough.

That is correct. Comment was the first and that remained, well caught.

OK, thanks! I'll get this committed sometime soon unless one of the other committers beats me to it.

Thanks again! Committed to 8.x.