@Test
	public void testOneAlt() throws Exception {
		LexerGrammar lg = new LexerGrammar(lexerText);
		Grammar g = new Grammar(
			"parser grammar T;\n" +
			"s : ID\n"+
			"  ;\n",
			lg);
		testInterp(lg, g, "s", "a",		"(s:1 a)");
	}
Tests to ensure GrammarParserInterpreter subclass of ParserInterpreter
 hasn't messed anything up.
tool-testsuite/test/org/antlr/v4/test/tool/TestGrammarParserInterpreter.java