code review 77580046: strings: fix Reader.UnreadRune

src/pkg/bytes/reader_test.go

 // Copyright 2012 The Go 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 bytes_test
 
 import (
         . "bytes"
         "fmt"
         "io"
@@ skipping 115 matching lines @@
                 t.Errorf("r.Len(): got %d, want %d", got, want)
         }
         if n, err := r.Read(make([]byte, 1)); err != nil || n != 1 {
                 t.Errorf("Read failed: read %d %v", n, err)
         }
         if got, want := r.Len(), 0; got != want {
                 t.Errorf("r.Len(): got %d, want %d", got, want)
         }
 }
 
+var UnreadRuneErrorTests = []struct {
+        name string
+        f    func(*Reader)
+}{
+        {"Read", func(r *Reader) { r.Read([]byte{}) }},
+        {"ReadAt", func(r *Reader) { r.ReadAt([]byte{}, 0) }},
+        {"ReadByte", func(r *Reader) { r.ReadByte() }},
+        {"UnreadRune", func(r *Reader) { r.UnreadRune() }},
+        {"Seek", func(r *Reader) { r.Seek(0, 1) }},
+        {"WriteTo", func(r *Reader) { r.WriteTo(&Buffer{}) }},
+}
+
+func TestUnreadRuneError(t *testing.T) {
+        for _, tt := range UnreadRuneErrorTests {
+                reader := NewReader([]byte("0123456789"))
+                if _, _, err := reader.ReadRune(); err != nil {
+                        // should not happen
+                        t.Fatal(err)
+                }
+                tt.f(reader)
+                err := reader.UnreadRune()
+                if err == nil {
+                        t.Errorf("Unreading after %s: expected error", tt.name)
+                }
+        }
+}
+
 func TestReaderDoubleUnreadRune(t *testing.T) {
         buf := NewBuffer([]byte("groucho"))
         if _, _, err := buf.ReadRune(); err != nil {
                 // should not happen
                 t.Fatal(err)
         }
         if err := buf.UnreadByte(); err != nil {
                 // should not happen
                 t.Fatal(err)
         }
@@ skipping 17 matching lines @@
         }
         discard := justWriter{ioutil.Discard} // hide ReadFrom
 
         var with, withOut nErr
         with.n, with.err = io.Copy(discard, NewReader(nil))
         withOut.n, withOut.err = io.Copy(discard, justReader{NewReader(nil)})
         if with != withOut {
                 t.Errorf("behavior differs: with = %#v; without: %#v", with, withOut)
         }
 }