JUnit setUp doesn't create object

Question

Why do I get a NullPointerExeption for testManuscript when trying to run my test?

This is my Manuscript.java:

package org.lhoffjann;


public class Manuscript {
private String msID;
private String path;
    public void setMSid(String msID){
        this.msID = msID;
    }

    public String getMSid() {
        return this.msID;
    }
}

This is my ManuscriptTest.java:

package org.lhoffjann;

import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.jupiter.api.Test;
import static org.junit.jupiter.api.Assertions.assertTrue;

public class ManuscriptTest {
    private static Manuscript testManuscript;

    @Before
    public void setUp(){
        testManuscript = new Manuscript();
    }
    @Test
    public void testGetMSid() {
        testManuscript.setMSid("1234");
        assertTrue("1234" == testManuscript.getMSid());
    }
}

A sidenote (both answers are excellent here): "1234" == testManuscript.getMSId() does not work - that is comparing reference identity, not value equality. It's "1234".equals(testManuscript.getMSid()), however, the better way is assertEquals("1234", testManuscript.getMSid()), as now JUnit will show you character-by-character where the differences are, if any. Also, getMSid() is not the proper style. It'd be getMsId(). Java code style dictates: .getDvdPlayer(), not .getDVDPlayer(). — rzwitserloot
– rzwitserloot, Commented Aug 28, 2022 at 9:27

Mark Rotteveel · Accepted Answer · 2022-08-28 08:07:51Z

5

You have imported @Test from JUnit 5, while you're using @Before from JUnit 4, that combination doesn't work. You need to choose which JUnit version you want to use, 4 or 5, and then consistently import classes from that JUnit version. I would recommend using JUnit 5, and removing all JUnit 4 dependencies from your classpath, or at least configure your IDE to not suggest those imports.

For this specific case, replace @Before (org.junit.Before) with @BeforeEach (org.junit.jupiter.api.BeforeEach).

In the example as shown, you don't even need this setUp method, as each test-execution gets its own instance of the test class. You can use:

private Manuscript testManuscript = new Manuscript();

That is, remove static, initialize the field directly, and remove the setUp method.

Even if you continue to use the setUp method, I recommend removing the static, so testManuscript is an instance field, like it is actually used.

edited Aug 28, 2022 at 8:07

answered Aug 28, 2022 at 7:46

Mark Rotteveel

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Comments

Michael Katt · Accepted Answer · 2022-08-28 08:43:11Z

You have mixed Junit4 with Junit5. You should use only one version.

Junit4 or

package org.lhoffjann;

import org.junit.Before;
import org.junit.Test;

import org.junit.Assert;

public class ManuscriptTest {
    private static Manuscript testManuscript;

    @Before
    public void setUp(){
        testManuscript = new Manuscript();
    }
    
    @Test
    public void testGetMSid() {
        testManuscript.setMSid("1234");
       Assert.assertEquals("1234",testManuscript.getMSid());
    }

or

Junit5

package org.lhoffjann;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

class ManuscriptTest {
    private static Manuscript testManuscript;

    @BeforeEach
    public void setUp() {
        testManuscript = new Manuscript();
    }

    @Test
    void testGetMSid() {
        testManuscript.setMSid("1234");
        Assertions.assertEquals("1234", testManuscript.getMSid());
    }
}

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