LexerInterpreter lexEngine = g.createLexerInterpreter(new ANTLRInputStream(input));
CommonTokenStream stream = new CommonTokenStream(lexEngine);
stream.fill();
TokenStreamRewriter tokens = new TokenStreamRewriter(stream);
tokens.replace(0, 2, "foo");
tokens.insertBefore(0, "z");
stream.fill();
// combine with left edge of rewrite
String result = tokens.getText();
String expecting = "zfoo";
assertEquals(expecting, result);