print how long the measured sleep time actually was on test failure

Author: RalfJung

src/tools/miri/tests/pass/concurrency/sync.rs

@@ -203,7 +203,8 @@ fn park_timeout() {
     // know Miri's timed synchronization primitives do not do that.
     // We allow much longer sleeps as well since the macOS GHA runners seem very oversubscribed
     // and sometimes just pause for 1 second or more.
-    assert!((200..2000).contains(&start.elapsed().as_millis()));
+    let elapsed = start.elapsed();
+    assert!((200..2000).contains(&elapsed.as_millis()), "bad sleep time: {:?}", elapsed);
 }
 
 fn park_unpark() {
@@ -222,7 +223,8 @@ fn park_unpark() {
     // know Miri's timed synchronization primitives do not do that.
     // We allow much longer sleeps as well since the macOS GHA runners seem very oversubscribed
     // and sometimes just pause for 1 second or more.
-    assert!((200..2000).contains(&start.elapsed().as_millis()));
+    let elapsed = start.elapsed();
+    assert!((200..2000).contains(&elapsed.as_millis()), "bad sleep time: {:?}", elapsed);
 
     t2.join().unwrap();
 }