test: assert container extension is created and memoized

Mutation testing showed all five mutants of the getContainerExtension()
condition survived: the extension type was never asserted and repeated
calls recreating the extension went unnoticed. One test asserting the
concrete type and instance identity on a second call kills all five.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: turegjorup

CHANGELOG.md

@@ -9,6 +9,11 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- Dev: added a test for `ItkDevOpenIdConnectBundle::getContainerExtension()`
+  asserting the custom extension is created and memoized (same instance on
+  repeated calls), prompted by mutation testing findings. No effect on the
+  published package.
+
 - CI: bumped `codecov/codecov-action` from `v5` to `v7` (restores Codecov's
   GPG signing key after the `codecovsecurity` account was removed, and moves
   the bundled `github-script` to Node 24) and set `fail_ci_if_error: false`

tests/ItkDevOpenIdConnectBundleTest.php

@@ -4,6 +4,8 @@
 
 use ItkDev\OpenIdConnectBundle\Command\UserLoginCommand;
 use ItkDev\OpenIdConnectBundle\Controller\LoginController;
+use ItkDev\OpenIdConnectBundle\DependencyInjection\ItkDevOpenIdConnectExtension;
+use ItkDev\OpenIdConnectBundle\ItkDevOpenIdConnectBundle;
 use ItkDev\OpenIdConnectBundle\Security\CliLoginTokenAuthenticator;
 use ItkDev\OpenIdConnectBundle\Security\OpenIdConfigurationProviderManager;
 use ItkDev\OpenIdConnectBundle\Security\OpenIdLoginAuthenticator;
@@ -57,4 +59,18 @@ public function testServiceWiring(): void
         $authenticator = $container->get(CliLoginTokenAuthenticator::class);
         $this->assertInstanceOf(CliLoginTokenAuthenticator::class, $authenticator);
     }
+
+    /**
+     * Test that the custom container extension is created and memoized.
+     */
+    public function testGetContainerExtension(): void
+    {
+        $bundle = new ItkDevOpenIdConnectBundle();
+
+        $extension = $bundle->getContainerExtension();
+        $this->assertInstanceOf(ItkDevOpenIdConnectExtension::class, $extension);
+
+        // Repeated calls must return the same instance, not recreate it.
+        $this->assertSame($extension, $bundle->getContainerExtension());
+    }
 }