Add "MkKeyContext" KeyContext generation function.

service/datastore/context_test.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package datastore
 
 import (
         "testing"
 
         "github.com/luci/gae/service/info"
@@ skipping 31 matching lines @@
                 Convey("without adding anything", func() {
                         So(Raw(c), ShouldBeNil)
                 })
 
                 Convey("adding a basic implementation", func() {
                         c = SetRaw(info.Set(c, fakeInfo{}), fakeService{})
 
                         Convey("lets you pull them back out", func() {
                                 So(Raw(c), ShouldResemble, &checkFilter{
                                         RawInterface: fakeService{},
-                                        kc:           KeyContext{"s~aid", "ns"},
+                                        kc:           MkKeyContext("s~aid", "ns"),
                                 })
                         })
 
                         Convey("and lets you add filters", func() {
                                 c = AddRawFilters(c, func(ic context.Context, rds RawInterface) RawInterface {
                                         return fakeFilt{rds}
                                 })
 
                                 curs, err := DecodeCursor(c, "pants")
                                 So(err, ShouldBeNil)
                                 So(curs.String(), ShouldEqual, "pants")
                         })
                 })
                 Convey("adding zero filters does nothing", func() {
                         So(AddRawFilters(c), ShouldEqual, c)
                 })
         })
 }