ICU-23325 Add a test case for the VTimeZone RRULE-UNTIL format issue.

Author: yumaoka

icu4c/source/test/intltest/tzrulets.cpp

@@ -140,6 +140,7 @@ void TimeZoneRuleTest::runIndexedTest( int32_t index, UBool exec, const char* &n
         CASE(15, TestT6669);
         CASE(16, TestVTimeZoneWrapper);
         CASE(17, TestT8943);
+        CASE(18, TestVTimeZoneRruleUntil);
         default: name = ""; break;
     }
 }
@@ -2656,6 +2657,26 @@ TimeZoneRuleTest::TestT8943() {
     delete rbtz;
 }
 
+// ICU-23325 UNTIL value in RRULE should be in ISO 8601 UTC format (e.g. 20211031T080000Z)
+// instead of local time (e.g. 20211031T020000).
+void
+TimeZoneRuleTest::TestVTimeZoneRruleUntil() {
+    IcuTestErrorCode ec(*this, "TestVTimeZoneRruleUntil");
+    LocalPointer<VTimeZone> vtz(VTimeZone::createVTimeZoneByID("America/Chihuahua"));
+    UDate start = getUTCMillis(2020, UCAL_JANUARY, 1);
+    // // RRULE lines for rule changes in 2022
+    UnicodeString rrule1 = UnicodeString("RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU;UNTIL=20211031T080000Z");
+    UnicodeString rrule2 = UnicodeString("RRULE:FREQ=YEARLY;BYMONTH=4;BYDAY=1SU;UNTIL=20220403T090000Z");
+
+    UnicodeString vtzData;
+    vtz->write(start, vtzData, ec);
+    ec.assertSuccess();
+    if (vtzData.indexOf(rrule1) < 0 ||
+        vtzData.indexOf(rrule2) < 0) {
+        errln("FAIL: RRULE UNTIL value is not in ISO 8601 UTC format");
+    }
+}
+
 #endif /* #if !UCONFIG_NO_FORMATTING */
 
 //eof

icu4c/source/test/intltest/tzrulets.h

@@ -40,6 +40,7 @@ class TimeZoneRuleTest : public CalendarTimeZoneTest {
     void TestT6669();
     void TestVTimeZoneWrapper();
     void TestT8943();
+    void TestVTimeZoneRruleUntil();
 
 private:
     void verifyTransitions(BasicTimeZone& icutz, UDate start, UDate end);

icu4j/main/core/src/test/java/com/ibm/icu/dev/test/timezone/TimeZoneRuleTest.java

@@ -2241,4 +2241,25 @@ public void TestT8943() {
             errln("Fail: Exception thrown - " + e.getMessage());
         }
     }
+
+    // ICU-23325 UNTIL value in RRULE should be in ISO 8601 UTC format (e.g. 20211031T080000Z)
+    // instead of local time (e.g. 20211031T020000).
+    @Test
+    public void TestVTimeZoneRruleUntil() {
+        final VTimeZone vtz = VTimeZone.create("America/Chihuahua");
+        final long start = getUTCMillis(2022, Calendar.JANUARY, 1);
+        // RRULE lines for rule changes in 2022
+        final String rrule1 = "RRULE:FREQ=YEARLY;BYMONTH=10;BYDAY=-1SU;UNTIL=20211031T080000Z";
+        final String rrule2 = "RRULE:FREQ=YEARLY;BYMONTH=4;BYDAY=1SU;UNTIL=20220403T090000Z";
+
+        try (StringWriter sw = new StringWriter()) {
+            vtz.write(sw, start);
+            String vtzStr = sw.toString();
+            logln(vtzStr);
+            assertTrue("Should contains " + rrule1, vtzStr.contains(rrule1));
+            assertTrue("Should contains " + rrule2, vtzStr.contains(rrule2));
+        } catch (IOException e) {
+            errln("IOException: " + e.getMessage());
+        }
+    }
 }