Better attempt at an appengine wrapper.

go/src/infra/gae/libs/wrapper/brokenfeatures_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 wrapper
+
+import (
+        "fmt"
+        "sync"
+        "testing"
+
+        . "github.com/smartystreets/goconvey/convey"
+)
+
+type foo struct {
+        *BrokenFeatures

[M-A Ruel, 2015/05/27 12:31:46]

It doesn't need to be a pointer anymore.
Everywhere.

[iannucci, 2015/05/27 17:06:55]

yep done

+}
+
+func (f *foo) halp() error { // test the ability to call IsBroken from an internal helper
+        return f.IsBroken()
+}
+
+func (f *foo) Foo() (string, error) {
+        err := f.halp()
+        if err != nil {
+                return "", err
+        }
+        return "foo", nil
+}
+
+func (f *foo) Bar() (string, error) {
+        err := f.halp()
+        if err != nil {
+                return "", err
+        }
+        return "bar", nil
+}
+
+type override struct {
+        *BrokenFeatures
+        totallyRekt bool
+}
+
+func (o *override) IsBroken() error {
+        if o.totallyRekt {
+                return fmt.Errorf("totallyRekt")
+        }
+        return o.BrokenFeatures.IsBroken()
+}
+
+func (o *override) Foo() error {
+        return o.IsBroken()
+}
+
+func TestBrokenFeatures(t *testing.T) {
+        e := fmt.Errorf("sup")

[M-A Ruel, 2015/05/27 12:31:46]

errors.New

[iannucci, 2015/05/27 17:06:55]

done

+        eCustom := fmt.Errorf("bad stuff happened")
+        f := foo{&BrokenFeatures{DefaultError: e}}
+
+        Convey("BrokenFeatures", t, func() {

[M-A Ruel, 2015/05/27 12:31:46]

Frankly, each could be a small test case and it'd be more readable, as I noted
to Vadim, not a fan of Convey.

[iannucci, 2015/05/27 17:06:55]

I actually disagree, and I'm a fan of Convey (now that I've rewritten their core
logic) :)

+                Convey("can break functions", func() {
+                        s, err := f.Foo()
+                        So(s, ShouldEqual, "foo")
+                        So(err, ShouldBeNil)
+
+                        f.BreakFeatures(nil, "Foo")
+                        _, err = f.Foo()
+                        So(err, ShouldEqual, e)
+
+                        Convey("and unbreak them", func() {
+                                f.UnbreakFeatures("Foo")
+                                s, err = f.Foo()
+                                So(s, ShouldEqual, "foo")
+                                So(err, ShouldBeNil)
+                        })
+
+                        Convey("and breaking features doesn't break unrelated ones", func() {
+                                s, err := f.Bar()
+                                So(s, ShouldEqual, "bar")
+                                So(err, ShouldBeNil)
+                        })
+                })
+
+                Convey("Can override IsBroken too", func() {
+                        o := &override{&BrokenFeatures{DefaultError: e}, false}
+                        Convey("Can break functions as normal", func() {
+                                o.BreakFeatures(nil, "Foo")
+                                So(o.Foo(), ShouldEqual, e)
+
+                                Convey("but can also break them in a user defined way", func() {
+                                        o.totallyRekt = true
+                                        So(o.Foo().Error(), ShouldContainSubstring, "totallyRekt")
+                                })
+                        })
+                })
+
+                Convey("Not specifying a default gets you a generic error", func() {
+                        f.BrokenFeatures.DefaultError = nil
+                        f.BreakFeatures(nil, "Foo")
+                        _, err := f.Foo()
+                        So(err.Error(), ShouldContainSubstring, `"Foo"`)
+                })
+
+                Convey("Can override the error returned", func() {
+                        f.BreakFeatures(eCustom, "Foo")
+                        v, err := f.Foo()
+                        So(v, ShouldEqual, "")
+                        So(err, ShouldEqual, eCustom)
+                })
+
+                Convey("Can be broken if not embedded", func() {
+                        err := error(nil)

[M-A Ruel, 2015/05/27 12:31:46]

I often use
var err error
var wg sync.WaitGroup

for uninitialized local variables. I don't mind much.

[iannucci, 2015/05/27 17:06:55]

done

+                        wg := sync.WaitGroup{}
+                        wg.Add(1)
+                        go func() {
+                                defer wg.Done()
+                                bf := &BrokenFeatures{DefaultError: e}

[M-A Ruel, 2015/05/27 12:31:46]

doesn't need to be a pointer.

[iannucci, 2015/05/27 17:06:55]

done

+                                // break some feature so we're forced to crawl the stack.
+                                bf.BreakFeatures(nil, "Nerds")
+                                // should break because there's no exported functions on the stack.
+                                err = bf.IsBroken()

[M-A Ruel, 2015/05/27 12:31:46]

With Convey, you can do checks in other goroutines? Bleh.

[iannucci, 2015/05/27 17:06:55]

done, I just didn't do it before

+                        }()
+                        wg.Wait()
+                        So(err, ShouldEqual, ErrBrokenFeaturesBroken)
+                })
+        })
+}