Merge pull request #3213 from alainjobart/disco

Fixing race condition in discovery test.

go/vt/discovery/topology_watcher_test.go

@@ -50,6 +50,13 @@ func checkWatcher(t *testing.T, cellTablets bool) {
 		t.Logf(`tw = ShardReplicationWatcher(topo.Server{ft}, fhc, "aa", "keyspace", "shard", 10ms, 5)`)
 	}
 
+	// Wait for the initial topology load to finish. Otherwise we
+	// have a background loadTablets() that's running, and it can
+	// interact with our tests in weird ways.
+	if err := tw.WaitForInitialTopology(); err != nil {
+		t.Fatalf("initial WaitForInitialTopology failed")
+	}
+
 	// add a tablet to the topology
 	ft.AddTablet("aa", 0, "host1", map[string]int32{"vt": 123})
 	tw.loadTablets()
@@ -198,7 +205,16 @@ func (ft *fakeTopo) GetShardReplication(ctx context.Context, cell, keyspace, sha
 func (ft *fakeTopo) GetTablet(ctx context.Context, alias *topodatapb.TabletAlias) (*topodatapb.Tablet, int64, error) {
 	ft.mu.RLock()
 	defer ft.mu.RUnlock()
-	return ft.tablets[topoproto.TabletAliasString(alias)], 0, nil
+	// Note we want to be correct here. The way we call this, we never
+	// change the tablet list in between a call to list them,
+	// and a call to get the record, so we could just blindly return it.
+	// (It wasn't the case before we added the WaitForInitialTopology()
+	// call in the test though!).
+	tablet, ok := ft.tablets[topoproto.TabletAliasString(alias)]
+	if !ok {
+		return nil, 0, topo.ErrNoNode
+	}
+	return tablet, 0, nil
 }
 
 func TestFilterByShard(t *testing.T) {