Ensure that the directory doesn't already exist

tests/Command/GenerateDrupal7ModuleCommandTest.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Opdavies\Tests\DrupalModuleGenerator\Command;
+
+use Opdavies\DrupalModuleGenerator\Command\GenerateDrupal7Command;
+use Opdavies\DrupalModuleGenerator\Exception\CannotCreateModuleException;
+use Symfony\Component\Console\Tester\CommandTester;
+use PHPUnit\Framework\TestCase;
+
+class GenerateDrupal7ModuleCommandTest extends TestCase
+{
+    /** @test */
+    public function it_throws_an_exception_if_the_directory_already_exists() {
+        mkdir('my-existing-drupal-module');
+
+        try {
+            $commandTester = new CommandTester(new GenerateDrupal7Command());
+            $commandTester->execute([
+                'module-name' => 'my-existing-drupal-module',
+            ]);
+        } catch (CannotCreateModuleException $e) {
+            $this->addToAssertionCount(1);
+        }
+
+        rmdir('my-existing-drupal-module');
+    }
+}