Verify SFTP retries when dealing with peer resets

This verifies that Flysystem SFTP adapter goes through all the
configured tries before throwing an `UnableToConnectToSftpHost`
exception.

Reverting the fix applied in
#1451 makes the test to
fail due to a unexpected `RuntimeException`.

Applying this for phpseclib v2 is a bit tricky, though, due to the lack
of knowledge on what has happened in the flow (e.g. `false` is returned
when a connection cannot be established or when an authentication error
happened). To make it work, the adapter for that version would need to
verify if there's a connection or not all the time - which doesn't sound
very good to me.

src/PhpseclibV3/SftpConnectionProviderTest.php

@@ -4,6 +4,7 @@
 
 namespace League\Flysystem\PhpseclibV3;
 
+use League\Flysystem\AdapterTestUtilities\ToxiproxyManagement;
 use phpseclib3\Net\SFTP;
 use PHPUnit\Framework\TestCase;
 
@@ -241,6 +242,52 @@ public function providing_an_invalid_password(): void
         $provider->provideConnection();
     }
 
+    /**
+     * @test
+     */
+    public function retries_several_times_until_failure(): void
+    {
+        $connectivityChecker = new class implements ConnectivityChecker {
+            /** @var int */
+            public $calls = 0;
+
+            public function isConnected(SFTP $connection): bool
+            {
+                ++$this->calls;
+
+                return $connection->isConnected();
+            }
+        };
+
+        $managesConnectionToxics = ToxiproxyManagement::forServer();
+        $managesConnectionToxics->resetPeerOnRequest('sftp', 10);
+
+        $maxTries = 5;
+
+        $provider = SftpConnectionProvider::fromArray(
+            [
+                'host' => 'localhost',
+                'username' => 'bar',
+                'privateKey' => __DIR__ . '/../../test_files/sftp/id_rsa',
+                'passphrase' => 'secret',
+                'port' => 8222,
+                'maxTries' => $maxTries,
+                'timeout' => 1,
+                'connectivityChecker' => $connectivityChecker,
+            ]
+        );
+
+        $this->expectException(UnableToConnectToSftpHost::class);
+
+        try {
+            $provider->provideConnection();
+        } finally {
+            $managesConnectionToxics->removeAllToxics();
+
+            self::assertSame($maxTries + 1, $connectivityChecker->calls);
+        }
+    }
+
     private function computeFingerPrint(string $publicKey): string
     {
         $content = explode(' ', $publicKey, 3);