test/reactor: add tests for early timers

Ensure that reactor timers fire at or after the
scheduled timeout.

src/common/libflux/test/reactor.c

@@ -226,6 +226,8 @@ static void oneshot (flux_reactor_t *r, flux_watcher_t *w,
 static void test_timer (flux_reactor_t *reactor)
 {
     flux_watcher_t *w;
+    double t0, t[] = { 0.001, 0.010, 0.100, 1.000 };
+    int i, rc;
 
     errno = 0;
     ok (!flux_timer_watcher_create (reactor, -1, 0, oneshot, NULL)
@@ -237,10 +239,12 @@ static void test_timer (flux_reactor_t *reactor)
     ok ((w = flux_timer_watcher_create (reactor, 0, 0, oneshot, NULL)) != NULL,
         "timer: creating zero timeout works");
     flux_watcher_start (w);
+    t0 = flux_reactor_now (reactor);
     ok (flux_reactor_run (reactor, 0) == 0,
         "timer: reactor ran to completion (single oneshot)");
     ok (oneshot_ran == true,
-        "timer: oneshot was executed");
+        "timer: oneshot was executed after %.3fs",
+        flux_reactor_now (reactor) - t0);
     oneshot_ran = false;
     ok (flux_reactor_run (reactor, 0) == 0,
         "timer: reactor ran to completion (expired oneshot)");
@@ -255,16 +259,32 @@ static void test_timer (flux_reactor_t *reactor)
     flux_watcher_stop (w);
     flux_watcher_destroy (w);
 
-    ok ((w = flux_timer_watcher_create (reactor, 0.01, 0.01, repeat, NULL))
+    ok ((w = flux_timer_watcher_create (reactor, 0.001, 0.001, repeat, NULL))
         != NULL,
         "timer: creating 1ms timeout with 1ms repeat works");
     flux_watcher_start (w);
+    t0 = flux_reactor_now (reactor);
     ok (flux_reactor_run (reactor, 0) == 0,
         "timer: reactor ran to completion (single repeat)");
     ok (repeat_countdown == 0,
         "timer: repeat timer stopped itself after countdown");
     flux_watcher_stop (w);
     flux_watcher_destroy (w);
+
+    oneshot_errno = 0;
+    ok ((w = flux_timer_watcher_create (reactor, 0, 0, oneshot, NULL)) != NULL,
+        "timer: creating timer watcher works");
+    for (i = 0; i < sizeof (t) / sizeof (t[0]); i++) {
+        flux_timer_watcher_reset (w, t[i], 0);
+        flux_watcher_start (w);
+        t0 = flux_reactor_now (reactor);
+        oneshot_ran = false;
+        rc = flux_reactor_run (reactor, 0);
+        double elapsed = flux_reactor_now (reactor) - t0;
+        ok (rc == 0 && oneshot_ran && elapsed >= t[i],
+            "timer: reactor ran %.3fs oneshot at >= time (%.3fs)", t[i], elapsed);
+    }
+
 }