test: add WaitFor func

Change-Id: I3d60ea9701721f9107da5322521a3c742d340646

pkg/test/wait.go

@@ -0,0 +1,33 @@
+/*
+Copyright 2013 Google Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package test
+
+import "time"
+
+// WaitFor returns true if condition returns true before maxWait.
+// It is checked immediately, and then every checkInterval.
+func WaitFor(condition func() bool, maxWait, checkInterval time.Duration) bool {
+	t0 := time.Now()
+	tmax := t0.Add(maxWait)
+	for time.Now().Before(tmax) {
+		if condition() {
+			return true
+		}
+		time.Sleep(checkInterval)
+	}
+	return false
+}