diff --git a/Tests/phpunit/BootstrapTest.php b/Tests/phpunit/BootstrapTest.php
index d1386c6..0874c08 100644
--- a/Tests/phpunit/BootstrapTest.php
+++ b/Tests/phpunit/BootstrapTest.php
@@ -27,6 +27,8 @@ class BootstrapTest extends TestCase
      * Unit test.
      *
      * @return void
+     *
+     * @coversNothing
      */
     public function test(): void
     {
diff --git a/Tests/phpunit/SplStringTest.php b/Tests/phpunit/SplStringTest.php
index bb9d4a6..0f69cd3 100644
--- a/Tests/phpunit/SplStringTest.php
+++ b/Tests/phpunit/SplStringTest.php
@@ -50,6 +50,17 @@ public function testConcatenate(): void
         $this->assertSame('hello world', $instance());
     }
 
+    /**
+     * Unit test.
+     *
+     * @return void
+     */
+    public function testStringCast(): void
+    {
+        $instance = new DuckString('hello world');
+        $this->assertSame('hello world', (string) $instance);
+    }
+
     /**
      * Unit test.
      *
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index 729ad4a..104cdbc 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -9,6 +9,7 @@
       <directory>./Tests</directory>
       <directory>./vendor</directory>
       <file>./.php-cs-fixer.dist.php</file>
+      <file>./bootstrap.php</file>
     </exclude>
     <report>
       <clover outputFile="build/logs/clover.xml"/>