Junit test cases for private method in Java reflection API

I have written the below Junit test cases to test private method using java reflection. I have skipped few statement in UserException.java.

Hope it will help you.

1. ValidatorTest.java

   import java.lang.reflect.InvocationTargetException;
   import java.lang.reflect.Method;
   
   import org.junit.Before;
   import org.junit.Rule;
   import org.junit.Assert;
   import org.junit.Test;
   import org.junit.rules.ExpectedException;
   
   import com.test.enums.ErrorMessage;
   import com.test.exception.UserException;
   import com.test.utils.Validator;
   
   public class ValidatorTest {
       Object validatorObject;
       Method method;
   
       @Before
       public void setUp() throws Exception {
           Class<Validator> validatorClass = Validator.class;
           validatorObject = validatorClass.newInstance();
           method = validatorObject.getClass().getDeclaredMethod(
                   "validateParam",
                   new Class[] { String.class, ErrorMessage.class });
           method.setAccessible(true);
       }
   
       @Rule
       private ExpectedException exception = ExpectedException.none();
   
       @Test(expected = UserException.class)
       public void testValidateException() throws Throwable {
           String inputForValidation = "PRASANT_ S\b\t\n\r";
           exception.expect(UserException.class);
           try {
               method.invoke(validatorObject, inputForValidation,
                       ErrorMessage.MY_ERROR_MESSAGE);
           } catch (InvocationTargetException | IllegalAccessException e) {
               throw e.getCause();
           }
       }
   
       @Test(expected = UserException.class)
       public void testValidateException2() throws InvocationTargetException,
               IllegalAccessException {
           String inputForValidation = "PRASANT @\b\t\n\r";
           exception.expect(UserException.class);
           try {
               method.invoke(validatorObject, inputForValidation,
                       ErrorMessage.MY_ERROR_MESSAGE);
           } catch (InvocationTargetException | IllegalAccessException e) {
               Assert.assertTrue("Input has invalid characters",
                       (e.getCause() instanceof UserException));
               throw (UserException) e.getCause();
           }
           Assert.fail("Invalid response");
       }
   
       @Test
       public void validatorTest() throws InvocationTargetException,
               IllegalAccessException {
           String inputForValidation = "PRASANT_S";
           method.invoke(validatorObject, inputForValidation,
                   ErrorMessage.MY_ERROR_MESSAGE);
           Assert.assertTrue(true);
       }
   }
   
   

2. Validator.java

   import org.slf4j.Logger;
   import org.slf4j.LoggerFactory;
   
   import com.test.enums.ErrorMessage;
   import com.test.exception.UserException;
   
   public class Validator {
       private static final Logger LOG = LoggerFactory.getLogger(Validator.class);
   
       @SuppressWarnings("unused")
       private void validateParam(String validateString,
               ErrorMessage errorMsg) throws UserException {
           StringBuilder invalidChars = new StringBuilder();
           for (int i = 0; i < validateString.length(); i++) {
               switch (validateString.charAt(i)) {
               case '\t': {
                   invalidChars.append('\t');
                   break;
               }
               case '\n': {
                   invalidChars.append('\n');
                   break;
               }
               case '\b': {
                   invalidChars.append('\b');
                   break;
               }
               case '\r': {
                   invalidChars.append('\r');
                   break;
               }
               }
           }
           if (invalidChars.length() != 0) {
               LOG.error(errorMsg.getMsg() + " " + invalidChars.toString());
               throw new UserException(errorMsg, invalidChars.toString());
           }
       }
   }
   
   

3. ErrorMessage.java

       public enum ErrorMessage {
           MY_ERROR_MESSAGE(490,"The invalid characters are ");
   
           private final int errorCode;
           private final String msg;
   
           private ErrorMessage(int errorCode,String msg){
               this.errorCode=errorCode;
               this.msg=msg;
           }
   
           public int getCode() {
               return errorCode;
           }
   
           public String getMsg() {
               return msg;
           }
   
           @Override
           public String toString(){
               return msg;
           }
       }
   
   

4. UserException.java

       public class UserException extends RuntimeException {
           private String errorMessage;
           private int errorCode = Response.Status.BAD_REQUEST.getStatusCode();
           private static final String DEFAULT_MESSAGE = "Bad request, please check url or request parameters";
   
           public UserException(ErrorMessage userMessage, String invChar) {
               if (userMessage != null) {
                   this.errorMessage = userMessage.getMsg() + " " + invChar;
                   this.errorCode = userMessage.getCode();
               }
           }
           ................
               ............
               ............
       }