code review 7808045: image/gif: make test repeatable

src/pkg/image/gif/reader_test.go

 package gif
 
 import (
         "bytes"
         "compress/lzw"
         "image"
         "image/color"
         "reflect"
         "testing"
 )
@@ skipping 96 matching lines @@
         var got string
         if err != nil {
                 got = err.Error()
         }
         if got != want {
                 t.Fatalf("got %v, want %v", got, want)
         }
 }
 
 func TestBounds(t *testing.T) {
-        // make a local copy of testGif
+        // make a local copy of testGIF
         gif := make([]byte, len(testGIF))
         copy(gif, testGIF)

[minux1, 2013/03/25 09:34:04]

is using append([]byte(nil), testGIF...) more idiomatic here?

[dave_cheney.net, 2013/03/26 05:20:29]

My personal feeling is it is not, I dislike using this append side effect. I am
happy to be overruled on this matter.

         // Make the bounds too big, just by one.
         gif[32] = 2
         want := "gif: frame bounds larger than image bounds"
         try(t, gif, want)
 
         // Make the bounds too small; does not trigger bounds
         // check, but now there's too much data.
         gif[32] = 0
         want = "gif: too much image data"
         try(t, gif, want)
         gif[32] = 1
 
         // Make the bounds really big, expect an error.
         want = "gif: frame bounds larger than image bounds"
         for i := 0; i < 4; i++ {
                 gif[32+i] = 0xff
         }
         try(t, gif, want)
 }