Milo: Increase test coverage for appengine/buildbot

milo/appengine/buildbot/html.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 buildbot
 
 import (
         "fmt"
         "net/http"
         "strconv"
@@ skipping 20 matching lines @@
                 common.ErrorPage(c, http.StatusBadRequest, "No build number")
                 return
         }
         num, err := strconv.Atoi(buildNum)
         if err != nil {
                 common.ErrorPage(c, http.StatusBadRequest,
                         fmt.Sprintf("%s does not look like a number", buildNum))
                 return
         }
 
-        result, err := build(c.Context, master, builder, num)
+        result, err := Build(c.Context, master, builder, num)
         if err != nil {
                 var code int
                 switch err {
                 case errBuildNotFound:
                         code = http.StatusNotFound
                 case errNotAuth:
                         code = http.StatusUnauthorized
                 default:
                         code = http.StatusInternalServerError
                 }
@@ skipping 24 matching lines @@
         if err != nil {
                 common.ErrorPage(c, http.StatusBadRequest, err.Error())
                 return
         }
         if limit < 0 {
                 limit = 25
         }
         cursor := c.Request.FormValue("cursor")
 
         result, err := builderImpl(c.Context, master, builder, limit, cursor)
-        if err != nil {
+        _, notFound := err.(errBuilderNotFound)
+        switch {
+        case err == nil:
+                templates.MustRender(c.Context, c.Writer, "pages/builder.html", templates.Args{
+                        "Builder": result,
+                })
+        case err == errNotAuth:
+                common.ErrorPage(c, http.StatusUnauthorized, err.Error())
+        case notFound:
+                common.ErrorPage(c, http.StatusNotFound, err.Error())
+        default: // err != nil
                 common.ErrorPage(c, http.StatusInternalServerError, err.Error())
-                return
         }
-
-        // Render into the template
-        templates.MustRender(c.Context, c.Writer, "pages/builder.html", templates.Args{
-                "Builder": result,
-        })
+        return
 }