Tests: Handle epoch date formatters edge cases (#34437)

This commit handles cases testing withLocale and withZone when the zone
and locale in question is the same as the special base case. This can
happen sometimes since the locale and zoneids are randomized.

server/src/test/java/org/elasticsearch/common/time/DateFormattersTests.java

@@ -23,6 +23,7 @@
 
 import java.time.Instant;
 import java.time.ZoneId;
+import java.time.ZoneOffset;
 import java.time.format.DateTimeParseException;
 import java.time.temporal.TemporalAccessor;
 import java.util.Locale;
@@ -130,23 +131,37 @@ public void testLocales() {
         assertThat(DateFormatters.forPattern("strict_date_optional_time").getLocale(), is(Locale.ROOT));
         Locale locale = randomLocale(random());
         assertThat(DateFormatters.forPattern("strict_date_optional_time").withLocale(locale).getLocale(), is(locale));
-        IllegalArgumentException e =
-            expectThrows(IllegalArgumentException.class, () -> DateFormatters.forPattern("epoch_millis").withLocale(locale));
-        assertThat(e.getMessage(), is("epoch_millis date formatter can only be in locale ROOT"));
-        e = expectThrows(IllegalArgumentException.class, () -> DateFormatters.forPattern("epoch_second").withLocale(locale));
-        assertThat(e.getMessage(), is("epoch_second date formatter can only be in locale ROOT"));
+        if (locale.equals(Locale.ROOT)) {
+            DateFormatter millisFormatter = DateFormatters.forPattern("epoch_millis");
+            assertThat(millisFormatter.withLocale(locale), is(millisFormatter));
+            DateFormatter secondFormatter = DateFormatters.forPattern("epoch_second");
+            assertThat(secondFormatter.withLocale(locale), is(secondFormatter));
+        } else {
+            IllegalArgumentException e =
+                expectThrows(IllegalArgumentException.class, () -> DateFormatters.forPattern("epoch_millis").withLocale(locale));
+            assertThat(e.getMessage(), is("epoch_millis date formatter can only be in locale ROOT"));
+            e = expectThrows(IllegalArgumentException.class, () -> DateFormatters.forPattern("epoch_second").withLocale(locale));
+            assertThat(e.getMessage(), is("epoch_second date formatter can only be in locale ROOT"));
+        }
     }
 
     public void testTimeZones() {
         // zone is null by default due to different behaviours between java8 and above
         assertThat(DateFormatters.forPattern("strict_date_optional_time").getZone(), is(nullValue()));
         ZoneId zoneId = randomZone();
         assertThat(DateFormatters.forPattern("strict_date_optional_time").withZone(zoneId).getZone(), is(zoneId));
-        IllegalArgumentException e =
-            expectThrows(IllegalArgumentException.class, () -> DateFormatters.forPattern("epoch_millis").withZone(zoneId));
-        assertThat(e.getMessage(), is("epoch_millis date formatter can only be in zone offset UTC"));
-        e = expectThrows(IllegalArgumentException.class, () -> DateFormatters.forPattern("epoch_second").withZone(zoneId));
-        assertThat(e.getMessage(), is("epoch_second date formatter can only be in zone offset UTC"));
+        if (zoneId.equals(ZoneOffset.UTC)) {
+            DateFormatter millisFormatter = DateFormatters.forPattern("epoch_millis");
+            assertThat(millisFormatter.withZone(zoneId), is(millisFormatter));
+            DateFormatter secondFormatter = DateFormatters.forPattern("epoch_second");
+            assertThat(secondFormatter.withZone(zoneId), is(secondFormatter));
+        } else {
+            IllegalArgumentException e =
+                expectThrows(IllegalArgumentException.class, () -> DateFormatters.forPattern("epoch_millis").withZone(zoneId));
+            assertThat(e.getMessage(), is("epoch_millis date formatter can only be in zone offset UTC"));
+            e = expectThrows(IllegalArgumentException.class, () -> DateFormatters.forPattern("epoch_second").withZone(zoneId));
+            assertThat(e.getMessage(), is("epoch_second date formatter can only be in zone offset UTC"));
+        }
     }
 
     public void testEqualsAndHashcode() {