diff --git a/src/Test/MakerTestDetails.php b/src/Test/MakerTestDetails.php
index 3d174028b..7e5854aa5 100644
--- a/src/Test/MakerTestDetails.php
+++ b/src/Test/MakerTestDetails.php
@@ -72,7 +72,7 @@ public function changeRootNamespace(string $rootNamespace): self
 
     public function addExtraDependencies(string ...$packages): self
     {
-        $this->extraDependencies += $packages;
+        $this->extraDependencies = [...$this->extraDependencies, ...$packages];
 
         return $this;
     }
@@ -125,11 +125,11 @@ public function getDependencies(): array
     {
         $depBuilder = $this->getDependencyBuilder();
 
-        return array_merge(
-            $depBuilder->getAllRequiredDependencies(),
-            $depBuilder->getAllRequiredDevDependencies(),
-            $this->extraDependencies
-        );
+        return [
+            ...$depBuilder->getAllRequiredDependencies(),
+            ...$depBuilder->getAllRequiredDevDependencies(),
+            ...$this->extraDependencies,
+        ];
     }
 
     public function getExtraDependencies(): array
diff --git a/tests/Test/MakerTestDetailsTest.php b/tests/Test/MakerTestDetailsTest.php
new file mode 100644
index 000000000..db600f12f
--- /dev/null
+++ b/tests/Test/MakerTestDetailsTest.php
@@ -0,0 +1,93 @@
+<?php
+
+/*
+ * This file is part of the Symfony MakerBundle package.
+ *
+ * (c) Fabien Potencier <fabien@symfony.com>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace Symfony\Bundle\MakerBundle\Tests\Test;
+
+use PHPUnit\Framework\TestCase;
+use Symfony\Bundle\MakerBundle\ConsoleStyle;
+use Symfony\Bundle\MakerBundle\DependencyBuilder;
+use Symfony\Bundle\MakerBundle\Generator;
+use Symfony\Bundle\MakerBundle\InputConfiguration;
+use Symfony\Bundle\MakerBundle\MakerInterface;
+use Symfony\Bundle\MakerBundle\Test\MakerTestDetails;
+use Symfony\Component\Console\Command\Command;
+use Symfony\Component\Console\Input\InputInterface;
+use Symfony\Component\Routing\Route;
+use Symfony\Component\Security\Core\Authorization\Voter\Voter;
+
+class MakerTestDetailsTest extends TestCase
+{
+    public function testAddExtraDependencies(): void
+    {
+        $details = new MakerTestDetails($this->createMock(MakerInterface::class));
+
+        $details->addExtraDependencies('twig');
+
+        self::assertSame(['twig'], $details->getExtraDependencies());
+
+        $details->addExtraDependencies('ux', 'mercure');
+
+        self::assertSame(['twig', 'ux', 'mercure'], $details->getExtraDependencies());
+    }
+
+    public function testAddRequiredPackageVersions(): void
+    {
+        $details = new MakerTestDetails($this->createMock(MakerInterface::class));
+
+        $details->addRequiredPackageVersion('twig', '4.x');
+
+        self::assertSame([['name' => 'twig', 'version_constraint' => '4.x']], $details->getRequiredPackageVersions());
+
+        $details->addRequiredPackageVersion('maker', '1.x');
+        self::assertSame([
+            ['name' => 'twig', 'version_constraint' => '4.x'],
+            ['name' => 'maker', 'version_constraint' => '1.x'],
+        ], $details->getRequiredPackageVersions());
+    }
+
+    public function testGetDependencies(): void
+    {
+        $details = new MakerTestDetails(new TestMakerFixture());
+
+        $details->addExtraDependencies('twig');
+
+        self::assertSame(['security', 'router', 'twig'], $details->getDependencies());
+    }
+}
+
+/**
+ * @method string getCommandDescription()
+ */
+class TestMakerFixture implements MakerInterface
+{
+    public function configureDependencies(DependencyBuilder $dependencies): void
+    {
+        $dependencies->addClassDependency(Voter::class, 'security');
+        $dependencies->addClassDependency(Route::class, 'router', devDependency: true);
+    }
+
+    public static function getCommandName(): string
+    {
+        return 'test';
+    }
+
+    public function configureCommand(Command $command, InputConfiguration $inputConfig)
+    {
+    }
+
+    public function interact(InputInterface $input, ConsoleStyle $io, Command $command)
+    {
+    }
+
+    public function generate(InputInterface $input, ConsoleStyle $io, Generator $generator)
+    {
+    }
+}