Dúvidas em testes com junit

Estou desenvolvendo testes com junit mas aparece o seguinte erro: java.lang.NullPointerException. Alguém pode me ajudar por favor?

package br.com.sofist.auction.domain;

import java.util.Calendar;
import java.util.List;
import org.assertj.core.api.Assertions;
import org.hamcrest.Matchers;
import org.junit.After;
import org.junit.AfterClass;
import org.junit.Test;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertThat;
import org.junit.Before;
import org.junit.BeforeClass;

/**
Test class to Auction
@see br.com.sofist.auction.domain.Auction
**/
public class AuctionTest {

@BeforeClass
public static void setUpClass() throws Exception {
}

@AfterClass
public static void tearDownClass() throws Exception {
}

@Before
public void setUp() throws Exception {
}

@After
public void tearDown() throws Exception {
}


/**
 * Test of propose method, of class Auction.
 */
@Test
public void testPropose() {
    System.out.println("propose");
    Bid auction = null;
    Auction instance = null;
    instance.propose(auction);
    
}

/**
 * Test of getDescription method, of class Auction.
 */
@Test
public void testGetDescription() {
    System.out.println("getDescription");
    Auction instance = null;
    String expResult = "";
    String result = instance.getDescription();
    assertEquals(expResult, result);
   
}

/**
 * Test of getBids method, of class Auction.
 */
@Test
public void testGetBids_0args() {
    System.out.println("getBids");
    Auction instance = null;
    List<Bid> expResult = null;
    List<Bid> result = instance.getBids();
    assertEquals(expResult, result);
   
}

/**
 * Test of getDate method, of class Auction.
 */
@Test
public void testGetDate() {
    System.out.println("getDate");
    Auction instance = null;
    Calendar expResult = null;
    Calendar result = instance.getDate();
    assertEquals(expResult, result);
   
}

/**
 * Test of close method, of class Auction.
 */
@Test
public void testClose() {
    System.out.println("close");
    Auction instance = null;
    instance.close();
    
}

/**
 * Test of isClosed method, of class Auction.
 */
@Test
public void testIsClosed() {
    System.out.println("isClosed");
    Auction instance = null;
    boolean expResult = false;
    boolean result = instance.isClosed();
    assertEquals(expResult, result);
   
}

/**
 * Test of setId method, of class Auction.
 */
@Test
public void testSetId() {
    System.out.println("setId");
    int id = 0;
    Auction instance = null;
    instance.setId(id);
    
}

/**
 * Test of getId method, of class Auction.
 */
@Test
public void testGetId() {
    System.out.println("getId");
    Auction instance = null;
    int expResult = 0;
    int result = instance.getId();
    assertEquals(expResult, result);
    
}

/**
 * Test of getBids method, of class Auction.
 */
@Test
public void testGetBids_int() {
    System.out.println("getBids");
    int i = 0;
    Auction instance = null;
    Object expResult = null;
    Object result = instance.getBids(i);
    assertEquals(expResult, result);
   
}

}

Não duplique tópicos:

Tópico trancado.