@Test public void testValidEscapeSequences() {
		String grammar =
			"lexer grammar A;\n" +
			"NORMAL_ESCAPE : '\\b \\t \\n \\f \\r \\' \\\\';\n" +
			"UNICODE_ESCAPE : '\\u0001 \\u00A1 \\u00a1 \\uaaaa \\uAAAA';\n";
		String expected =
			"";

		String[] pair = new String[] {
			grammar,
			expected
		};

		testErrors(pair, true);
	}
This test ensures that the {@link ErrorType#INVALID_ESCAPE_SEQUENCE}
error is not reported for escape sequences that are known to be valid.
tool-testsuite/test/org/antlr/v4/test/tool/TestToolSyntaxErrors.java