snapshot: Separate tests using root from non-root

Signed-off-by: Samuel Karp <skarp@amazon.com>

snapshot/testutil/helpers.go

@@ -1,13 +1,34 @@
 package testutil
 
 import (
+	"flag"
+	"os"
 	"syscall"
 	"testing"
+
+	"github.com/stretchr/testify/assert"
 )
 
+var rootEnabled bool
+
+func init() {
+	flag.BoolVar(&rootEnabled, "test.root", false, "enable tests that require root")
+}
+
+// Unmount unmounts a given mountPoint and sets t.Error if it fails
 func Unmount(t *testing.T, mountPoint string) {
 	t.Log("unmount", mountPoint)
 	if err := syscall.Unmount(mountPoint, 0); err != nil {
 		t.Error("Could not umount", mountPoint, err)
 	}
 }
+
+// RequiresRoot skips tests that require root, unless the test.root flag has
+// been set
+func RequiresRoot(t *testing.T) {
+	if !rootEnabled {
+		t.Skip("skipping test that requires root")
+		return
+	}
+	assert.Equal(t, 0, os.Getuid(), "This test must be run as root.")
+}