Fix error message from KeyForObj when passing an invalid struct.

service/datastore/properties_test.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package datastore
 
 import (
         "math"
         "testing"
         "time"
@@ skipping 134 matching lines @@
                                 pm := PropertyMap{"": {MkProperty("trap!")}}
                                 _, err := pm.GetMeta("foo")
                                 So(err, ShouldEqual, ErrMetaFieldUnset)
 
                                 err = pm.SetMeta("foo", 100)
                                 So(err, ShouldBeNil)
 
                                 v, err := pm.GetMeta("foo")
                                 So(err, ShouldBeNil)
                                 So(v, ShouldEqual, 100)
-                                So(pm.GetMetaDefault("foo", 100), ShouldEqual, 100)
-                                So(pm.GetMetaDefault("bar", 100), ShouldEqual, 100)
+
+                                v, err = GetMetaDefault(pm, "foo", 100)
+                                So(err, ShouldBeNil)
+                                So(v, ShouldEqual, 100)
+
+                                v, err = GetMetaDefault(pm, "bar", 100)
+                                So(err, ShouldBeNil)
+                                So(v, ShouldEqual, 100)
 
                                 npm, err := pm.Save(false)
                                 So(err, ShouldBeNil)
                                 So(len(npm), ShouldEqual, 0)
                         })
 
                         Convey("errors", func() {
                                 Convey("too many values", func() {
                                         pm := PropertyMap{
                                                 "$bad": {MkProperty(100), MkProperty(200)},
                                         }
                                         _, err := pm.GetMeta("bad")
                                         So(err.Error(), ShouldContainSubstring, "too many values")
                                 })
 
                                 Convey("weird value", func() {
                                         pm := PropertyMap{}
                                         err := pm.SetMeta("sup", complex(100, 20))
                                         So(err.Error(), ShouldContainSubstring, "bad type")
                                 })
                         })
                 })
         })
 }