@Test public void testNotCharSetWithString() throws Exception {
		// might be a useful feature to add someday
		String[] pair = new String[] {
			"grammar T;\n" +
			"a : A {System.out.println($A.text);} ;\n" +
			"A : ~('a'|'aa') ;\n" +
			"B : 'b' ;\n",
			"error(" + ErrorType.INVALID_LITERAL_IN_LEXER_SET.code + "): T.g4:3:10: multi-character literals are not allowed in lexer sets: 'aa'\n"
		};
		testErrors(pair, true);
	}
Test errors with the set stuff in lexer and parser
tool-testsuite/test/org/antlr/v4/test/tool/TestErrorSets.java