Add util/test package

test/poll.go

@@ -0,0 +1,26 @@
+package test
+
+import (
+	"reflect"
+	"testing"
+	"time"
+)
+
+// Poll repeatedly evaluates condition until we either timeout, or it succeeds.
+func Poll(t testing.TB, d time.Duration, want interface{}, have func() interface{}) {
+	t.Helper()
+	deadline := time.Now().Add(d)
+	for {
+		if time.Now().After(deadline) {
+			break
+		}
+		if reflect.DeepEqual(want, have()) {
+			return
+		}
+		time.Sleep(d / 100)
+	}
+	h := have()
+	if !reflect.DeepEqual(want, h) {
+		t.Fatalf("expected %v, got %v", want, h)
+	}
+}