1 files changed, 49 insertions, 0 deletions
diff --git a/src/pkg/bytes/reader_test.go b/src/pkg/bytes/reader_test.go
index 2e4b1f26e..f0a3e26c4 100644
--- a/src/pkg/bytes/reader_test.go
+++ b/src/pkg/bytes/reader_test.go
@@ -8,6 +8,7 @@ import (
 	. "bytes"
 	"fmt"
 	"io"
+	"io/ioutil"
 	"os"
 	"testing"
 )
@@ -86,3 +87,51 @@ func TestReaderAt(t *testing.T) {
 		}
 	}
 }
+
+func TestReaderWriteTo(t *testing.T) {
+	for i := 0; i < 30; i += 3 {
+		var l int
+		if i > 0 {
+			l = len(data) / i
+		}
+		s := data[:l]
+		r := NewReader(testBytes[:l])
+		var b Buffer
+		n, err := r.WriteTo(&b)
+		if expect := int64(len(s)); n != expect {
+			t.Errorf("got %v; want %v", n, expect)
+		}
+		if err != nil {
+			t.Errorf("for length %d: got error = %v; want nil", l, err)
+		}
+		if b.String() != s {
+			t.Errorf("got string %q; want %q", b.String(), s)
+		}
+		if r.Len() != 0 {
+			t.Errorf("reader contains %v bytes; want 0", r.Len())
+		}
+	}
+}
+
+// verify that copying from an empty reader always has the same results,
+// regardless of the presence of a WriteTo method.
+func TestReaderCopyNothing(t *testing.T) {
+	type nErr struct {
+		n   int64
+		err error
+	}
+	type justReader struct {
+		io.Reader
+	}
+	type justWriter struct {
+		io.Writer
+	}
+	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)
+	}
+}