Autoload test directories

[opdavies]

Problem

I've been evaluating Phpactor recently whilst working on Drupal projects and found that I was getting a There are no class name candidates error when trying to create a new class.

After installing this plugin and dumping an updated autoloader, creating a class within a module's src directory worked, but it still couldn't generate a test class within the tests/src directory.

Solution

Reviewing the autoload_psr4.php file, I could see that the module's src directory was being loaded correctly but the tests/src directory wasn't included.

After adding one manually to confirm it fixed the issue, I've created this PR that checks for a tests/src directory within each module and if one exists, adds it to the expected Drupal\\Tests\\ namespace`.