1 files changed, 61 insertions, 0 deletions
diff --git a/src/bufio/bufio_test.go b/src/bufio/bufio_test.go
index ff3396e9469..b3456d23411 100644
--- a/src/bufio/bufio_test.go
+++ b/src/bufio/bufio_test.go
@@ -762,6 +762,67 @@ func TestWriteString(t *testing.T) {
 	}
 }
 
+func TestWriteStringStringWriter(t *testing.T) {
+	const BufSize = 8
+	{
+		tw := &teststringwriter{}
+		b := NewWriterSize(tw, BufSize)
+		b.WriteString("1234")
+		tw.check(t, "", "")
+		b.WriteString("56789012")   // longer than BufSize
+		tw.check(t, "12345678", "") // but not enough (after filling the partially-filled buffer)
+		b.Flush()
+		tw.check(t, "123456789012", "")
+	}
+	{
+		tw := &teststringwriter{}
+		b := NewWriterSize(tw, BufSize)
+		b.WriteString("123456789")   // long string, empty buffer:
+		tw.check(t, "", "123456789") // use WriteString
+	}
+	{
+		tw := &teststringwriter{}
+		b := NewWriterSize(tw, BufSize)
+		b.WriteString("abc")
+		tw.check(t, "", "")
+		b.WriteString("123456789012345")      // long string, non-empty buffer
+		tw.check(t, "abc12345", "6789012345") // use Write and then WriteString since the remaining part is still longer than BufSize
+	}
+	{
+		tw := &teststringwriter{}
+		b := NewWriterSize(tw, BufSize)
+		b.Write([]byte("abc")) // same as above, but use Write instead of WriteString
+		tw.check(t, "", "")
+		b.WriteString("123456789012345")
+		tw.check(t, "abc12345", "6789012345") // same as above
+	}
+}
+
+type teststringwriter struct {
+	write       string
+	writeString string
+}
+
+func (w *teststringwriter) Write(b []byte) (int, error) {
+	w.write += string(b)
+	return len(b), nil
+}
+
+func (w *teststringwriter) WriteString(s string) (int, error) {
+	w.writeString += s
+	return len(s), nil
+}
+
+func (w *teststringwriter) check(t *testing.T, write, writeString string) {
+	t.Helper()
+	if w.write != write {
+		t.Errorf("write: expected %q, got %q", write, w.write)
+	}
+	if w.writeString != writeString {
+		t.Errorf("writeString: expected %q, got %q", writeString, w.writeString)
+	}
+}
+
 func TestBufferFull(t *testing.T) {
 	const longString = "And now, hello, world! It is the time for all good men to come to the aid of their party"
 	buf := NewReaderSize(strings.NewReader(longString), minReadBufferSize)