Extract logic to determine which package manager

..is used

Always Composer for PHP.
npm, yarn or pnpm for node.

tests/DeterminePackageManagerTest.php

@@ -0,0 +1,94 @@
+<?php
+
+declare(strict_types=1);
+
+namespace App\Tests;
+
+use App\Action\DeterminePackageManager;
+use App\Action\DetermineProjectLanguage;
+use App\Action\DetermineProjectLanguageInterface;
+use App\Enum\PackageManager;
+use App\Enum\ProjectLanguage;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Filesystem\Filesystem;
+
+final class DeterminePackageManagerTest extends TestCase
+{
+    /** @test */
+    public function it_finds_php(): void
+    {
+        $filesystem = $this->createMock(Filesystem::class);
+        $filesystem
+            ->method('exists')
+            ->with('./composer.json')
+            ->willReturn(true);
+
+        $action = new DeterminePackageManager(
+            filesystem: $filesystem,
+            projectLanguage: ProjectLanguage::PHP->value,
+        );
+
+        self::assertSame(
+            actual: $action->getPackageManager(),
+            expected: PackageManager::Composer->value,
+        );
+    }
+
+    public function lockFileProvider(): array
+    {
+        return [
+            'npm' => [
+                './package-lock.json',
+                PackageManager::npm->value,
+                [
+                    ['./package-lock.json', true],
+                    ['./pnpm-lock.yaml', false],
+                    ['./yarn.lock', false],
+                ],
+            ],
+            'pnpm' => [
+                './pnpm-lock.yaml',
+                PackageManager::pnpm->value,
+                [
+                    ['./package-lock.json', false],
+                    ['./pnpm-lock.yaml', true],
+                    ['./yarn.lock', false],
+                ],
+            ],
+            'yarn' => [
+                './yarn.lock',
+                PackageManager::yarn->value,
+                [
+                    ['./package-lock.json', false],
+                    ['./pnpm-lock.yaml', false],
+                    ['./yarn.lock', true],
+                ],
+            ],
+        ];
+    }
+
+    /**
+     * @dataProvider lockFileProvider
+     * @test
+     */
+    public function it_finds_node(
+        string $lockFile,
+        string $expectedPackageManager,
+        array $valueMap,
+    ): void {
+        $filesystem = $this->createMock(Filesystem::class);
+        $filesystem
+            ->method('exists')
+            ->will(self::returnValueMap($valueMap));
+
+        $action = new DeterminePackageManager(
+            filesystem: $filesystem,
+            projectLanguage: ProjectLanguage::JavaScript->value,
+        );
+
+        self::assertSame(
+            actual: $action->getPackageManager(),
+            expected: $expectedPackageManager,
+        );
+    }
+}