diff --git a/composer.json b/composer.json
index d7df4a23..1e2b6673 100644
--- a/composer.json
+++ b/composer.json
@@ -17,7 +17,7 @@
         "guzzlehttp/psr7": "~1.1"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8 || ^5.7",
+        "phpunit/phpunit": "^4.8 || ^5.7 || ^7.5.15",
         "mockery/mockery": "~0.9.2"
     },
     "suggest": {
diff --git a/tests/FileTest.php b/tests/FileTest.php
index 820a18af..e1c01fd2 100644
--- a/tests/FileTest.php
+++ b/tests/FileTest.php
@@ -19,7 +19,7 @@ class FileTest extends TestCase
     public function testBasePath()
     {
         $file = new File;
-        $this->assertNull(null, $file->basePath());
+        $this->assertNull(null, $file->basePath() ?: '');
 
         $file->dirname = 'foo';
         $file->basename = 'bar';