diff --git a/src/Roots/Acorn/Bootloader.php b/src/Roots/Acorn/Bootloader.php
index 34d8764a..16dcfa48 100644
--- a/src/Roots/Acorn/Bootloader.php
+++ b/src/Roots/Acorn/Bootloader.php
@@ -26,6 +26,13 @@ class Bootloader
      */
     protected $app;
 
+    /**
+     * Filesystem helper
+     * 
+     * @var \Roots\Acorn\Filesystem\Filesystem
+     */
+    protected $files;
+
     /**
      * Base path for the application
      *
@@ -61,9 +68,10 @@ public static function getInstance(ApplicationContract $app = null)
     /**
      * Create a new bootloader instance.
      */
-    public function __construct(ApplicationContract $app = null)
+    public function __construct(ApplicationContract $app = null, Filesystem $files = null)
     {
         $this->app = $app;
+        $this->files = $files ?? new Filesystem;
 
         static::$instance ??= $this;
     }
@@ -301,7 +309,7 @@ protected function basePath(): string
 
             is_dir($app_path = get_theme_file_path('app')) => dirname($app_path),
 
-            $vendor_path = (new Filesystem())->closest(dirname(__DIR__, 4), 'composer.json') => dirname($vendor_path),
+            is_file($vendor_path = $this->files->closest(dirname(__DIR__, 4), 'composer.json')) => dirname($vendor_path),
 
             default => dirname(__DIR__, 3)
         };
@@ -399,12 +407,11 @@ protected function fallbackPath(string $path): string
      */
     protected function fallbackStoragePath()
     {
-        $files = new Filesystem();
         $path = WP_CONTENT_DIR.DIRECTORY_SEPARATOR.'cache'.DIRECTORY_SEPARATOR.'acorn';
-        $files->ensureDirectoryExists($path.DIRECTORY_SEPARATOR.'framework'.DIRECTORY_SEPARATOR.'cache'.DIRECTORY_SEPARATOR.'data', 0755, true);
-        $files->ensureDirectoryExists($path.DIRECTORY_SEPARATOR.'framework'.DIRECTORY_SEPARATOR.'views', 0755, true);
-        $files->ensureDirectoryExists($path.DIRECTORY_SEPARATOR.'framework'.DIRECTORY_SEPARATOR.'sessions', 0755, true);
-        $files->ensureDirectoryExists($path.DIRECTORY_SEPARATOR.'logs', 0755, true);
+        $this->files->ensureDirectoryExists($path.DIRECTORY_SEPARATOR.'framework'.DIRECTORY_SEPARATOR.'cache'.DIRECTORY_SEPARATOR.'data', 0755, true);
+        $this->files->ensureDirectoryExists($path.DIRECTORY_SEPARATOR.'framework'.DIRECTORY_SEPARATOR.'views', 0755, true);
+        $this->files->ensureDirectoryExists($path.DIRECTORY_SEPARATOR.'framework'.DIRECTORY_SEPARATOR.'sessions', 0755, true);
+        $this->files->ensureDirectoryExists($path.DIRECTORY_SEPARATOR.'logs', 0755, true);
 
         return $path;
     }
diff --git a/tests/Application/BootloaderTest.php b/tests/Application/BootloaderTest.php
index 7133916d..e7ac06aa 100644
--- a/tests/Application/BootloaderTest.php
+++ b/tests/Application/BootloaderTest.php
@@ -3,8 +3,63 @@
 use Roots\Acorn\Bootloader;
 use Roots\Acorn\Tests\Test\TestCase;
 
+use function Roots\Acorn\Tests\mock;
+
 uses(TestCase::class);
 
+beforeEach(function () {
+    unset($_ENV['APP_BASE_PATH']);
+});
+
 it('should get a new instance', function () {
     expect(Bootloader::getInstance())->toBeInstanceOf(Bootloader::class);
 });
+
+it('should reuse the same instance', function () {
+    expect(Bootloader::getInstance())->toBe(Bootloader::getInstance());
+});
+
+it('should get a new application instance', function () {
+    expect((new Bootloader)->getApplication())->toBeInstanceOf(\Illuminate\Contracts\Foundation\Application::class);
+});
+
+it('should set the basePath if env var is set', function () {
+    $_ENV['APP_BASE_PATH'] = $path = $this->fixture('base_path/base_empty');
+
+    $app = (new Bootloader)->getApplication();
+
+    expect($app->basePath())->toBe($path);
+});
+
+it('should set the basePath if composer.json exists in theme', function () {
+    $composer_path = $this->fixture('base_path/base_composer');
+    
+    $this->stub('get_theme_file_path', fn ($path) => "{$composer_path}/{$path}");
+
+    $app = (new Bootloader)->getApplication();
+
+    expect($app->basePath())->toBe($composer_path);
+});
+
+it('should set the basePath if app exists in theme', function () {
+    $app_path = $this->fixture('base_path/base_app');
+    $this->stub('get_theme_file_path', fn () => $app_path);
+
+    $app = Bootloader::getInstance()->getApplication();
+
+    expect($app->basePath())->toBe(dirname($app_path));
+});
+
+it('should set the basePath if composer.json exists as ancestor of ../../../', function () {
+    $files = mock(\Roots\Acorn\Filesystem\Filesystem::class);
+    $this->stub('get_theme_file_path', fn () => '');
+
+    $composer_path = $this->fixture('base_path/base_composer');
+
+    $files->shouldReceive('closest')->andReturn("{$composer_path}/composer.json");
+    $files->shouldReceive('ensureDirectoryExists');
+
+    $app = (new Bootloader(null, $files))->getApplication();
+
+    expect($app->basePath())->toBe($composer_path);
+});
diff --git a/tests/Application/__fixtures__/base_path/base_app/app/.gitignore b/tests/Application/__fixtures__/base_path/base_app/app/.gitignore
new file mode 100644
index 00000000..d6b7ef32
--- /dev/null
+++ b/tests/Application/__fixtures__/base_path/base_app/app/.gitignore
@@ -0,0 +1,2 @@
+*
+!.gitignore
diff --git a/tests/Application/__fixtures__/base_path/base_composer/composer.json b/tests/Application/__fixtures__/base_path/base_composer/composer.json
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/Application/__fixtures__/base_path/base_empty/.gitignore b/tests/Application/__fixtures__/base_path/base_empty/.gitignore
new file mode 100644
index 00000000..d6b7ef32
--- /dev/null
+++ b/tests/Application/__fixtures__/base_path/base_empty/.gitignore
@@ -0,0 +1,2 @@
+*
+!.gitignore
diff --git a/tests/Application/__fixtures__/use_paths/composer.json b/tests/Application/__fixtures__/use_paths/composer.json
new file mode 100644
index 00000000..e69de29b
diff --git a/tests/Helpers.php b/tests/Helpers.php
index 6ebb0962..d114e0cd 100644
--- a/tests/Helpers.php
+++ b/tests/Helpers.php
@@ -28,9 +28,7 @@ function temp(string $path = null)
     if (! $temp) {
         $temp = (new TemporaryDirectory())->create();
 
-        register_shutdown_function(function () use ($temp) {
-            $temp->delete();
-        });
+        register_shutdown_function(fn () => $temp->delete());
     }
 
     if ($path !== null) {