diff --git a/src/test/java/jp/ne/paypay/api/ApiClientTest.java b/src/test/java/jp/ne/paypay/api/ApiClientTest.java
index 2aa21f6..33d5886 100644
--- a/src/test/java/jp/ne/paypay/api/ApiClientTest.java
+++ b/src/test/java/jp/ne/paypay/api/ApiClientTest.java
@@ -86,6 +86,18 @@ public void configTest() throws ApiException{
 
     }
 
+    @Test
+    public void parameterToStringTest(){
+        List<String> params = new ArrayList<>();
+        params.add("Id");
+        params.add("Name");
+        String parameterToString = apiClient.parameterToString(params);
+        Assert.assertEquals(parameterToString, "Id,Name");
+        Date date  = new GregorianCalendar(2020, Calendar.FEBRUARY, 5).getTime();
+        parameterToString = apiClient.parameterToString(date);
+        Assert.assertTrue(parameterToString.startsWith("2020-"));
+    }
+
     @Test
     public void perfModeTest(){
         apiClient.setPerfMode(true);