diff --git a/tests/unit/Framework/AssertTest.php b/tests/unit/Framework/AssertTest.php
index 8fa34c3b46f..d00c6cb4fba 100644
--- a/tests/unit/Framework/AssertTest.php
+++ b/tests/unit/Framework/AssertTest.php
@@ -113,6 +113,20 @@ public function testAssertContainsEmptyStringInString(): void
         $this->assertContains('', 'test');
     }
 
+    public function testAssertStringContainsNonString(): void
+    {
+        $this->expectException(Exception::class);
+
+        $this->assertContains(null, '');
+    }
+
+    public function testAssertStringNotContainsNonString(): void
+    {
+        $this->expectException(Exception::class);
+
+        $this->assertNotContains(null, '');
+    }
+
     public function testAssertArrayHasKeyThrowsExceptionForInvalidFirstArgument(): void
     {
         $this->expectException(Exception::class);