fix(tests): isolate databases in memory and reject persistent connections

tests/README.md

@@ -0,0 +1,17 @@
+# Database isolation
+
+Run the suite with `composer test` or `vendor/bin/phpunit`. Both use
+`tests/bootstrap.php`, which forces SQLite `:memory:` in all environment sources.
+Tests never need a MySQL test database or the local database credentials.
+
+`Tests\TestCase` rejects cached configuration and validates the default connection
+before application providers boot. Its connection factory also rejects persistent
+databases, URLs, and alternate endpoints for named or dynamically built connections.
+Tests that need Laravel must extend this base class. Do not bypass these guards to
+make a failing test pass; adapt database-specific tests to SQLite or use a separately
+designed disposable database workflow.
+
+`php tests/verify-database-safety.php` checks the guard and application wiring without
+running test setup, queries, migrations, or opening PDO connections.
+
+The suite does not validate MySQL-specific behavior when using SQLite.