astutil: add new broken test

Tests will still pass because it's marked as known broken,
but it will log the unexpected for now.

R=golang-dev, crawshaw
CC=golang-dev
https://golang.org/cl/27330043

astutil/imports_test.go

@@ -35,6 +35,7 @@ type test struct {
 	pkg        string
 	in         string
 	out        string
+	broken     bool // known broken
 }
 
 var addTests = []test{
@@ -168,6 +169,27 @@ import (
 	fmtpkg "fmt"
 	"os"
 )
+`,
+	},
+	{
+		broken: true,
+		name:   "struct comment",
+		pkg:    "time",
+		in: `package main
+
+// This is a comment before a struct.
+type T struct {
+	t  time.Time
+}
+`,
+		out: `package main
+
+import "time"
+
+// This is a comment before a struct.
+type T struct {
+	t time.Time
+}
 `,
 	},
 }
@@ -177,9 +199,13 @@ func TestAddImport(t *testing.T) {
 		file := parse(t, test.name, test.in)
 		AddNamedImport(file, test.renamedPkg, test.pkg)
 		if got := print(t, test.name, file); got != test.out {
+			if test.broken {
+				t.Logf("%s is known broken:\ngot: %s\nwant: %s", test.name, got, test.out)
+			} else {
 				t.Errorf("%s:\ngot: %s\nwant: %s", test.name, got, test.out)
 			}
 		}
+	}
 }
 
 func TestDoubleAddImport(t *testing.T) {