make the repair_backoff test more robust (#1095)

* more the repair_backoff test more robust

* fix names and magic numbers

src/window.rs

@@ -1056,6 +1056,9 @@ mod test {
     }
     #[test]
     pub fn test_repair_backoff() {
+        let num_tests = 100;
+        let res: usize = (0..num_tests)
+            .map(|_| {
                 let mut last = 0;
                 let mut times = 0;
                 let total: usize = (0..127)
@@ -1067,12 +1070,16 @@ mod test {
                     .sum();
                 assert_eq!(times, 128);
                 assert_eq!(last, 1);
-        assert!(total > 0);
-        assert!(total < 127);
                 repair_backoff(&mut last, &mut times, 1);
                 assert_eq!(times, 64);
                 repair_backoff(&mut last, &mut times, 2);
                 assert_eq!(times, 2);
                 assert_eq!(last, 2);
+                total
+            })
+            .sum();
+        let avg = res / num_tests;
+        assert!(avg >= 3);
+        assert!(avg <= 5);
     }
 }