@Test public void testParserRuleNameStartingWithUnderscore() {
		String[] pair = new String[] {
			"grammar A;\n" +
			"_a : 'x' ;\n",

			"error(" + ErrorType.SYNTAX_ERROR.code + "): A.g4:2:0: syntax error: '_' came as a complete surprise to me\n"
		};
		testErrors(pair, true);
	}
This is a regression test for antlr/antlr4#262
"Parser Rule Name Starting With an Underscore"
https://github.com/antlr/antlr4/issues/262
tool-testsuite/test/org/antlr/v4/test/tool/TestToolSyntaxErrors.java