test: make harder for flaky test to fail

Author: edusperoni

test-app/app/src/main/assets/app/tests/testRuntimeImplementedAPIs.js

@@ -1,32 +1,33 @@
 describe("Runtime exposes", function () {
   it("__time a low overhead, high resolution, time in ms.", function () {
-    // Try to get the times using Date.now and __time and compare the results, expect them to be somewhat "close".
-    // Sometimes GC hits after Date.now is captured but before __time or the vice-versa and the test fails,
-    // so we are giving it several attempts.
-    for (var i = 0; i < 5; i++) {
-      try {
-        var dateTimeStart = Date.now();
-        var timeStart = __time();
-        var acc = 0;
-        var s = android.os.SystemClock.elapsedRealtime();
-        for (var i = 0; i < 1000; i++) {
-          var c = android.os.SystemClock.elapsedRealtime();
-          acc += c - s;
-          s = c;
-        }
-        var dateTimeEnd = Date.now();
-        var timeEnd = __time();
-        var dateDelta = dateTimeEnd - dateTimeStart;
-        var timeDelta = timeEnd - timeStart;
-        var tolerance = Math.max(10, dateDelta * 0.5);
-        expect(timeDelta > 0).toBe(true);
-        expect(Math.abs(dateDelta - timeDelta) < tolerance).toBe(true);
-        break;
-      } catch (e) {
-        if (i == 4) {
-          throw e;
-        }
+    // Compare the Date.now and __time deltas over the same interval and expect
+    // them to be somewhat "close". A GC pause or scheduler preemption landing
+    // between the capture of the two clocks skews a single measurement, so the
+    // window is kept wide enough for the proportional tolerance to absorb
+    // realistic pauses, and the measurement is retried a few times with the
+    // expectation only recorded once (jasmine expectations don't throw, so a
+    // try/catch based retry would record the failed attempts anyway).
+    var attempts = 5;
+    var dateDelta, timeDelta, tolerance;
+    var ok = false;
+
+    for (var attempt = 0; attempt < attempts && !ok; attempt++) {
+      var dateTimeStart = Date.now();
+      var timeStart = __time();
+
+      while (Date.now() - dateTimeStart < 50) {
+        // busy-wait to widen the measured interval
       }
+
+      var dateTimeEnd = Date.now();
+      var timeEnd = __time();
+
+      dateDelta = dateTimeEnd - dateTimeStart;
+      timeDelta = timeEnd - timeStart;
+      tolerance = Math.max(10, dateDelta * 0.5);
+      ok = timeDelta > 0 && Math.abs(dateDelta - timeDelta) < tolerance;
     }
+
+    expect(ok).toBe(true, "__time delta " + timeDelta + "ms diverged from Date.now delta " + dateDelta + "ms (tolerance " + tolerance + "ms) on all " + attempts + " attempts");
   });
 });