func TestWriteString(t *testing.T) {
	const BufSize = 8
	buf := new(strings.Builder)
	b := NewWriterSize(buf, BufSize)
	b.WriteString("0")                         // easy
	b.WriteString("123456")                    // still easy
	b.WriteString("7890")                      // easy after flush
	b.WriteString("abcdefghijklmnopqrstuvwxy") // hard
	b.WriteString("z")
	if err := b.Flush(); err != nil {
		t.Error("WriteString", err)
	}

		if x, ok := expr.(*ast.Ident); ok {
			expr = &ast.Ident{NamePos: pos, Name: x.Name}
		}

		// Change AST, because some later processing depends on it,
		// and also because -godefs mode still prints the AST.
		old := *r.Expr
		*r.Expr = expr

		// Record source-level edit for cgo output.
		if !r.Done {
			// Prepend a space in case the earlier code ends