Refactor a bit.

service/rawdatastore/context_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 rawdatastore
+
+import (
+        "errors"
+        "testing"
+
+        . "github.com/smartystreets/goconvey/convey"
+        "golang.org/x/net/context"
+)
+
+type fakeService struct{ Interface }
+
+type fakeFilt struct{ Interface }
+
+func (fakeFilt) Count(Query) (int, error) {
+        return 0, errors.New("wow")
+}
+
+func TestServices(t *testing.T) {
+        t.Parallel()
+
+        Convey("Test service interfaces", t, func() {
+                c := context.Background()
+                Convey("without adding anything", func() {
+                        So(Get(c), ShouldBeNil)
+                })
+
+                Convey("adding a basic implementation", func() {
+                        c = Set(c, fakeService{})
+
+                        Convey("lets you pull them back out", func() {
+                                So(Get(c), ShouldResemble, fakeService{})
+                        })
+
+                        Convey("and lets you add filters", func() {
+                                c = AddFilters(c, func(ic context.Context, rds Interface) Interface {
+                                        return fakeFilt{rds}
+                                })
+
+                                _, err := Get(c).Count(nil)
+                                So(err.Error(), ShouldEqual, "wow")
+                        })
+                })
+                Convey("adding zero filters does nothing", func() {
+                        So(AddFilters(c), ShouldEqual, c)
+                })
+        })
+}