Add test

src/datetime/tests.rs

@@ -313,6 +313,20 @@ fn test_datetime_offset() {
     assert!(*edt.with_ymd_and_hms(2014, 5, 6, 7, 8, 9).unwrap().offset() != est);
 }
 
+#[test]
+fn signed_duration_since_autoref() {
+    let dt1 = Utc.with_ymd_and_hms(2014, 5, 6, 7, 8, 9).unwrap();
+    let dt2 = Utc.with_ymd_and_hms(2014, 3, 4, 5, 6, 7).unwrap();
+    let diff1 = dt1.signed_duration_since(dt2);
+    // dt2 would no longer be available if `signed_duration_since` didn't use `Borrow`
+    let diff2 = dt2.signed_duration_since(dt1);
+    assert_eq!(diff1, -diff2);
+
+    let diff1 = dt1 - &dt2; // We can choose to substract rhs by reference
+    let diff2 = dt2 - dt1; // Or consume rhs
+    assert_eq!(diff1, -diff2);
+}
+
 #[test]
 fn test_datetime_date_and_time() {
     let tz = FixedOffset::east_opt(5 * 60 * 60).unwrap();