16663: Add comments in racy test.

Arvados-DCO-1.1-Signed-off-by: Tom Clegg <tom@tomclegg.ca>

diff --git a/lib/dispatchcloud/scheduler/sync_test.go b/lib/dispatchcloud/scheduler/sync_test.go
index ae264bb29887fa0bb65e092b655da76eec2fedd6..538f5ea8cfd0b9e14edec62d629eaa104ff70514 100644 (file)
--- a/lib/dispatchcloud/scheduler/sync_test.go
+++ b/lib/dispatchcloud/scheduler/sync_test.go
@@ -84,6 +84,14 @@ func (*SchedulerSuite) TestCancelOrphanedContainers(c *check.C) {
 
        // Sync shouldn't cancel the container because it might be
        // running on the VM with state=="unknown".
+       //
+       // (Cancel+forget happens asynchronously and requires multiple
+       // sync() calls, so even after 10x sync-and-sleep iterations,
+       // we aren't 100% confident that sync isn't trying to
+       // cancel. But in the test environment, the goroutines started
+       // by sync() access stubs and therefore run quickly, so it
+       // works fine in practice. We accept that if the code is
+       // broken, the test will still pass occasionally.)
        for i := 0; i < 10; i++ {
                sch.sync()
                time.Sleep(time.Millisecond)
@@ -94,6 +102,10 @@ func (*SchedulerSuite) TestCancelOrphanedContainers(c *check.C) {
 
        // Sync should cancel & forget the container when the
        // "unknown" node goes away.
+       //
+       // (As above, cancel+forget is async and requires multiple
+       // sync() calls, but stubs are fast so in practice this takes
+       // much less than 1s to complete.)
        pool.unknown = nil
        for deadline := time.Now().Add(time.Second); ; time.Sleep(time.Millisecond) {
                sch.sync()