diff --git a/tests/Mouson/Helpers/SequenceCalculator/QuintupleSequenceCalculatorTest.php b/tests/Mouson/Helpers/SequenceCalculator/QuintupleSequenceCalculatorTest.php
index 8163e28..2d60f1b 100644
--- a/tests/Mouson/Helpers/SequenceCalculator/QuintupleSequenceCalculatorTest.php
+++ b/tests/Mouson/Helpers/SequenceCalculator/QuintupleSequenceCalculatorTest.php
@@ -48,4 +48,19 @@ public function test_測試雙倍數列輸入2應回傳4()
         $this->assertEquals($expected, $actual);
     }
 
+    public function test_測試雙倍數列輸入負數應回傳兩倍負數()
+    {
+        /** Arrange */
+        $target = new QuintupleSequenceCalculator();
+        $value  = -2;
+        /** Assume */
+        $expected = -10;
+
+        /** Act */
+        $actual = $target->calculate($value);
+
+        /** Assert */
+        $this->assertEquals($expected, $actual);
+    }
+
 }