if p != j {
				t.Errorf("IndexByte(%q, %d) = %d", b[i:i+15], 100+j, p)
			}
		}
		for j := 0; j < 15; j++ {
			b[i+j] = 0
		}
	}
	// Make sure matches outside the slice never trigger.
	for i := 0; i <= len(b)-15; i++ {
		for j := 0; j < 15; j++ {
			b[i+j] = 1
		}
		for j := 0; j < 15; j++ {
			p := IndexByte(b[i:i+15], byte(0))
			if p != -1 {

	w.buf = append(w.buf, b...)
	w.readFromBytes += len(b)
	return int64(len(b)), err
}

// Test that calling (*Writer).ReadFrom with a partially-filled buffer
// fills the buffer before switching over to ReadFrom.
func TestWriterReadFromWithBufferedData(t *testing.T) {
	const bufsize = 16

	input := createTestInput(64)
	rfw := &readFromWriter{}
	w := NewWriterSize(rfw, bufsize)

	// insufficient; if the user specifies CGO_CFLAGS=-fdiagnostics-color,
	// GCC will ignore TERM, and GCC can also be configured at compile-time
	// to ignore TERM.)
	stderr := p.gccErrors(b.Bytes(), "-fdiagnostics-color=never")
	if strings.Contains(stderr, "unrecognized command line option") {
		// We're using an old version of GCC that doesn't understand
		// -fdiagnostics-color. Those versions can't print color anyway,