diff --git a/test/built-ins/Temporal/Instant/prototype/toString/timezone-string-datetime.js b/test/built-ins/Temporal/Instant/prototype/toString/timezone-string-datetime.js
index 7097708233..58be86f737 100644
--- a/test/built-ins/Temporal/Instant/prototype/toString/timezone-string-datetime.js
+++ b/test/built-ins/Temporal/Instant/prototype/toString/timezone-string-datetime.js
@@ -4,7 +4,6 @@
 /*---
 esid: sec-temporal.instant.prototype.tostring
 description: Conversion of ISO date-time strings to Temporal.TimeZone instances
-includes: [arrayContains.js]
 features: [Temporal]
 ---*/
 
@@ -16,30 +15,30 @@ assert.throws(RangeError, () => instance.toString({ timeZone: { timeZone } }), "
 
 timeZone = "2021-08-19T17:30Z";
 const result1 = instance.toString({ timeZone });
-arrayContains(result1, "UTC", "date-time + Z is UTC time zone");
+assert.sameValue(result1.substr(-6), "+00:00", "date-time + Z is UTC time zone");
 const result2 = instance.toString({ timeZone: { timeZone } });
-arrayContains(result2, "UTC", "date-time + Z is UTC time zone (string in property bag)");
+assert.sameValue(result2.substr(-6), "+00:00", "date-time + Z is UTC time zone (string in property bag)");
 
 timeZone = "2021-08-19T17:30-07:00";
 const result3 = instance.toString({ timeZone });
-arrayContains(result3, "-07:00", "date-time + offset is the offset time zone");
+assert.sameValue(result3.substr(-6), "-07:00", "date-time + offset is the offset time zone");
 const result4 = instance.toString({ timeZone: { timeZone } });
-arrayContains(result4, "-07:00", "date-time + offset is the offset time zone (string in property bag)");
+assert.sameValue(result4.substr(-6), "-07:00", "date-time + offset is the offset time zone (string in property bag)");
 
 timeZone = "2021-08-19T17:30[America/Vancouver]";
 const result5 = instance.toString({ timeZone });
-arrayContains(result5, "America/Vancouver", "date-time + IANA annotation is the IANA time zone");
+assert.sameValue(result5.substr(-6), "-08:00", "date-time + IANA annotation is the offset time zone");
 const result6 = instance.toString({ timeZone: { timeZone } });
-arrayContains(result6, "America/Vancouver", "date-time + IANA annotation is the IANA time zone (string in property bag)");
+assert.sameValue(result6.substr(-6), "-08:00", "date-time + IANA annotation is the offset time zone (string in property bag)");
 
 timeZone = "2021-08-19T17:30Z[America/Vancouver]";
 const result7 = instance.toString({ timeZone });
-arrayContains(result7, "America/Vancouver", "date-time + Z + IANA annotation is the IANA time zone");
+assert.sameValue(result7.substr(-6), "-08:00", "date-time + Z + IANA annotation is the offset time zone");
 const result8 = instance.toString({ timeZone: { timeZone } });
-arrayContains(result8, "America/Vancouver", "date-time + Z + IANA annotation is the IANA time zone (string in property bag)");
+assert.sameValue(result8.substr(-6), "-08:00", "date-time + Z + IANA annotation is the offset time zone (string in property bag)");
 
 timeZone = "2021-08-19T17:30-07:00[America/Vancouver]";
 const result9 = instance.toString({ timeZone });
-arrayContains(result9, "America/Vancouver", "date-time + offset + IANA annotation is the IANA time zone");
+assert.sameValue(result9.substr(-6), "-08:00", "date-time + offset + IANA annotation is the offset time zone");
 const result10 = instance.toString({ timeZone: { timeZone } });
-arrayContains(result10, "America/Vancouver", "date-time + offset + IANA annotation is the IANA time zone (string in property bag)");
+assert.sameValue(result10.substr(-6), "-08:00", "date-time + offset + IANA annotation is the offset time zone (string in property bag)");