Configuring the database and PHPUnit was described on the Laracasts Forum. How to use Artisan commands instead of Laravel's database migration trait to reset the database after each test was described on the ScriptScoop Forum.
Laravel 5.1's database migration trait crashes on migration rollback during test tear-down since the in-memory database is already destroyed at that point.
Directory structure:
./tests/MemoryDbTest.php
./config/database.php
./phpunit.xml