Add and use an action to get the project language

tests/ProjectLanguageTest.php

@@ -0,0 +1,58 @@
+<?php
+
+use App\Action\DetermineProjectLanguage;
+use App\Enum\ProjectLanguage;
+use PHPUnit\Framework\TestCase;
+use Symfony\Component\Filesystem\Filesystem;
+
+final class ProjectLanguageTest extends TestCase
+{
+    /**
+     * @test
+     * @testdox It identifies a PHP project if it has a composer.json file
+     */
+    public function it_identifies_a_php_project_if_it_has_a_composer_json_file(): void
+    {
+        $filesystem = $this->createMock(Filesystem::class);
+        $filesystem
+            ->method('exists')
+            ->with('./composer.json')
+            ->willReturn(true);
+
+        $action = new DetermineProjectLanguage(
+            filesystem: $filesystem,
+        );
+
+        self::assertSame(
+            actual: $action->getLanguage(),
+            expected: ProjectLanguage::PHP->value,
+        );
+    }
+
+    /**
+     * @test
+     * @testdox It identifies a node project if it has a package.json file
+     */
+    public function it_identifies_a_node_project_if_it_has_a_package_json_file(): void
+    {
+        // self::markTestSkipped();
+
+        $filesystem = $this->createMock(Filesystem::class);
+
+        $filesystem
+            ->method('exists')
+            ->will(self::returnValueMap([
+                ['./composer.json', false],
+                ['./package.json', true],
+            ]));
+
+        $action = new DetermineProjectLanguage(
+            filesystem: $filesystem,
+        );
+
+        self::assertSame(
+            actual: $action->getLanguage(),
+            expected: ProjectLanguage::JavaScript->value,
+        );
+    }
+}