title: How to do Unit testing using Junit4?
body: <p>I had created a JWTCreateImpl class given below to generate a jwt token using generatToken() method and respond a jwt string using loginUser() method. loginUser() method takes email and password as a parameter coming from frontend. This email is compare with email exist in database and if email is not present the errorResponse will become "email not exist" similarly do for password doesn't match. And lastly if email and password exist for a particular id then extracting the result from database and pass only uuid of user to generate a token and response will be jwt string. I want to perform unit testing for this class using Junit4, how can I write the test case using Junit4 for this?</p>
  
  <p>JWTCreateImpl class Implements JWTCreate Interface which Contains abstract Methods loginUser(UserInfoJWT userInfoJWT) and generateToken(UUID uuid) and one String JWT_TOKEN_KEY which is used in generateToken() method mainly use with HMAC256 Algorithm. UserInfoJWT is a POJO class Which contains email and password of user.</p>
  
  <p>ResponseJWT is a POJO class  which contains UserToken and errorResponse.</p>
  
  <pre><code>import com.auth0.jwt.JWT;
  import com.auth0.jwt.algorithms.Algorithm;
  import com.auth0.jwt.exceptions.JWTCreationException;
  import com.knoldus.magad.jwt.api.JWTCreate;
  import com.knoldus.magad.jwt.model.ResponseJWT;
  import com.knoldus.magad.jwt.model.UserInfoJWT;
  import com.knoldus.magad.dao.model.UserInfo;
  import com.knoldus.magad.user.api.UserInfoProcessingAPI;
  
  import org.apache.log4j.Logger;
  
  
  import java.io.UnsupportedEncodingException;
  import java.time.ZonedDateTime;
  import java.util.Date;
  import java.util.UUID;
  import java.util.concurrent.CompletableFuture;
  public class JWTCreateImpl implements JWTCreate {
  private static final Logger LOGGER = Logger.getLogger(JWTCreateImpl.class);
  private UserInfo existingUser;
  private ResponseJWT response;
  private  UserInfoProcessingAPI userInfoProcessingAPI;
  private static final String NO_USER_EMAIL = "Email doesn't exists..";
  private static  final String LOGIN_UNSUCCESSFUL = "Wrong Password";
  
  
  @Override
  public CompletableFuture&lt;String&gt;loginUser(final UserInfoJWT userInfoJWT) {
      return userInfoProcessingAPI.getUserInfo(userInfoJWT.getUserEmail()).thenApply(result -&gt; {
          existingUser = result.orElse(null);
          if (existingUser == null) {
              response = ResponseJWT.builder().errorResponse(NO_USER_EMAIL).build();
          } else {
              final String dataBasePassword = existingUser.getUserPassword();
              if (userInfoJWT.getUserPassword().equals(dataBasePassword)) {
                  response = ResponseJWT.builder().userToken(generateToken(existingUser.getUuid())).build();
              } else {
                  response = ResponseJWT.builder().errorResponse(LOGIN_UNSUCCESSFUL).build();
              }
          }
          return response.toString();
      });
  }
  @Override
  public String generateToken(final UUID uuid) {
      try {
          final Algorithm algorithm = Algorithm.HMAC256(JWT_TOKEN_KEY);
          final Date expirationDate = Date.from(ZonedDateTime.now().plusHours(24).toInstant());
          final Date issuedAt = Date.from(ZonedDateTime.now().toInstant());
          final String id = String.valueOf(uuid);
          final String issuer = "MagADAuth";
          return JWT.create()
                  .withIssuedAt(issuedAt) // Issue date.
                  .withExpiresAt(expirationDate) // Expiration date.
                  .withClaim("userId", id)
                  .withIssuer(issuer) // Issuer of the token.
                  .sign(algorithm); // And the signing algorithm.
      } catch (UnsupportedEncodingException | JWTCreationException e) {
          LOGGER.error(e.getMessage(), e);
      }
      return null;
  }
  </code></pre>