JUNIT Null Pointer Exception

问题

it's my first time using JUNIT and I literally cannot get it to work.

I've got a person class, in which has firstName and lastName, and a test class in which I need to test the methods. Everytime I attempt to test one though, if i've wrote a test for the particular method, it fails.

Here is my code.

Person Class

public class Person {
    private String firstName;
    private String lastName;    

    public Person (String a, String b) {
        firstName = a;
        lastName = b;
    }

    public String getfirstName() {
        return firstName;
    }

    public void setfirstName(String firstName) {
        this.firstName = firstName;
    }

    public String getlastName() {
        return lastName;
    }

    public void setlastName(String lastName) {
        this.lastName = lastName;
    }

    @Override
    public String toString() {
        return  firstName + " " + lastName;
    }
}

Person Test class

public class PersonTest {
    Person p1;

    public PersonTest() {
        Person p1 = new Person ("Thomas", "Brown");
    }

    @Before
    public void setUp() {}

    @After
    public void tearDown() {}

    @Test
    public void testGetfirstName() {
        assertEquals("Thomas", p1.getfirstName());
    }

    @Test
    public void testSetfirstName() {}

    @Test
    public void testGetlastName() {
        assertEquals("Brown", p1.getlastName());
    }

    @Test
    public void testSetlastName() {}

    @Test
    public void testToString() {
        assertEquals("Thomas Brown", p1.toString());
    }
}

Could anyone point me in the right direction?

回答1:

This is the right way to do it:

@Before
public void setUp() {
    p1 = new Person ("Thomas", "Brown");
}

You have 2 problems in your code.

public PersonTest() {
    Person p1 = new Person ("Thomas", "Brown");
}

This creates a local variable and your field p1 stays null.

The second is that in your setUp method you do not initialize p1.

The method you annotate with @Before will run before every test to you should put the initialization there. I also suggest to use more descriptive names so you should change p1 to target or something like that.

Edit: For your set... methods you can do something like this:

public class PersonTest {
    private static final String TEST_FIRST_NAME = "some name";

    Person target;

    // ...
    @Test
    public void testSetFirstName() {
        target.setFirstName(TEST_FIRST_NAME);
        Assert.assertEquals(target.getFirstName(), TEST_FIRST_NAME);
    }
}

At that point you can assume that getFirstName works since you have a test for it as well.

A sidenote: I think you don't have to test getters and setters as long as you generate them with Eclipse. It is just unnesessary.

回答2:

Change

Person p1 = new Person ("Thomas", "Brown"); //this is local variable

 p1 = new Person ("Thomas", "Brown");// and this will use the instance variable

来源：https://stackoverflow.com/questions/19978692/junit-null-pointer-exception

标签

java

testing

junit