tests: improve qzss coverage

Signed-off-by: Guillaume W. Bres <[email protected]>

tests/epoch.rs

@@ -1551,6 +1551,13 @@ fn test_time_of_week() {
         epoch_utc
     );
 
+    // GPST and QZSST share the same properties at all times
+    let epoch_qzsst = epoch.in_time_scale(TimeScale::QZSST);
+    assert_eq!(epoch.to_gregorian_utc(), epoch_qzsst.to_gregorian_utc());
+
+    let gps_qzss_offset = TimeScale::GPST.ref_epoch() - TimeScale::QZSST.ref_epoch();
+    assert_eq!(gps_qzss_offset.total_nanoseconds(), 0); // no offset
+
     // 06/01/1980 01:00:00 = 1H into GPST <=> (0, 3_618_000_000_000)
     let epoch = Epoch::from_time_of_week(0, 3_618_000_000_000, TimeScale::GPST);
     assert_eq!(epoch.to_gregorian_utc(), (1980, 01, 06, 01, 00, 0 + 18, 00));