Add unittest coverage for boottime_util_linux.go

pkg/kubelet/util/BUILD

@@ -9,6 +9,7 @@ load(
 go_test(
     name = "go_default_test",
     srcs = [
+        "bootime_util_linux_test.go",
         "util_test.go",
         "util_unix_test.go",
         "util_windows_test.go",

pkg/kubelet/util/bootime_util_linux_test.go

@@ -0,0 +1,36 @@
+// +build freebsd linux
+
+/*
+Copyright 2018 The Kubernetes Authors.
+
+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 util
+
+import (
+	"testing"
+	"time"
+)
+
+func TestGetBootTime(t *testing.T) {
+	boottime, err := GetBootTime()
+
+	if err != nil {
+		t.Errorf("Unable to get system uptime")
+	}
+
+	if !boottime.After(time.Time{}) {
+		t.Errorf("Invalid system uptime")
+	}
+}