### Question:
MessageCount { public static boolean isValidExpression(String value) { String trimValue = value.replaceAll(" ", ""); return EXPRESSION_PATTERN.matcher(trimValue).matches(); } private  MessageCount(int count, Operation op); private  MessageCount(Range range); static MessageCount fromString(String value); static void main(String[] args); static boolean isValidExpression(String value); int getCount(); Operation getOperation(); boolean checkInt(int i); @Override String toString();  }### Answer:
@Test public void testIsValidExpression() throws Exception { checkIsValidExpression("${ref.field}"); checkIsValidExpression("${ref.field[1]}"); checkIsValidExpression("${ref.field.field}"); checkIsValidExpression("${ref.field[1].field}"); checkIsValidExpression("${ref.field1} + ${ref.field2}"); checkIsValidExpression("${ref.field1} + ${ref.field2} + 100"); checkIsValidExpression("${ref.field1} + ${ref.field2} + ${ref.field3}"); for (Operation operation : Operation.values()) { checkIsValidExpression(operation.getValue() + " ${ref.field}"); } checkIntervalExpression("${ref.field}", "${ref.field} + 123", "${ref.field} - 123", "${ref.field} * 123", "${ref.field} / 123", "(${ref.field} + 123)", "123"); }