Tweaks the RefreshDatabase trait for better support of multi-dbs

When working with multiple databases and some of them are in-memory
while others are regular disk-based databases, we usually have to
override some of the traits methods to make it work. Also, the database
restoration process doesn't handle multiple DBs that well.

With these changes, when an app needs to support multiple databases, the
user will have to do a few steps:

1. Set the `$connectionsToTransact` protected property on the TestCase
listing all connections they use
1. Override the `migrateDatabase` method and call all the migrate:fresh
commands for all their connections

Restoring the databases between tests should now be completely handled
by the trait, no matter which database connection uses in-memory
databases or not.

Author: tonysm

src/Illuminate/Foundation/Testing/RefreshDatabase.php

@@ -18,7 +18,7 @@ public function refreshDatabase()
     {
         $this->beforeRefreshingDatabase();
 
-        if ($this->usingInMemoryDatabase()) {
+        if ($this->usingInMemoryDatabases()) {
             $this->restoreInMemoryDatabase();
         }
 
@@ -32,11 +32,23 @@ public function refreshDatabase()
      *
      * @return bool
      */
-    protected function usingInMemoryDatabase()
+    protected function usingInMemoryDatabase(string $name)
     {
-        $default = config('database.default');
+        return config("database.connections.{$name}.database") === ':memory:';
+    }
 
-        return config("database.connections.$default.database") === ':memory:';
+    /**
+     * Determines if any of the connections transacting is using in-memory databases.
+     */
+    protected function usingInMemoryDatabases(): bool
+    {
+        foreach ($this->connectionsToTransact() as $name) {
+            if (config("database.connections.{$name}.database") === ':memory:') {
+                return true;
+            }
+        }
+
+        return false;
     }
 
     /**
@@ -63,7 +75,7 @@ protected function restoreInMemoryDatabase()
     protected function refreshTestDatabase()
     {
         if (! RefreshDatabaseState::$migrated) {
-            $this->artisan('migrate:fresh', $this->migrateFreshUsing());
+            $this->migrateDatabases();
 
             $this->app[Kernel::class]->setArtisan(null);
 
@@ -89,7 +101,7 @@ public function beginDatabaseTransaction()
 
             $connection->setTransactionManager($transactionsManager);
 
-            if ($this->usingInMemoryDatabase()) {
+            if ($this->usingInMemoryDatabase($name)) {
                 RefreshDatabaseState::$inMemoryConnections[$name] ??= $connection->getPdo();
             }
 
@@ -121,7 +133,15 @@ public function beginDatabaseTransaction()
     protected function connectionsToTransact()
     {
         return property_exists($this, 'connectionsToTransact')
-                            ? $this->connectionsToTransact : [null];
+                            ? $this->connectionsToTransact : [config('database.default')];
+    }
+
+    /**
+     * Perform the database migration command.
+     */
+    protected function migrateDatabases(): void
+    {
+        $this->artisan('migrate:fresh', $this->migrateFreshUsing());
     }
 
     /**