How to test if a variable exists using JUnit 5?

Question

I would like to test to see if a variable exists in JUnit testing.

I have a class called animal which is an abstract class.


public abstract class Animal {
    private final int age;
    private final int speed;
    
    public Animal (int age,int speed) {
        this.age = age;
        this.speed = speed;
    }
    public static void main(String[] args) {
    }
    @Override 
    public boolean equals(Object anotherObject) {
           if (this == anotherObject) {  
                  return true;  
              }else {
                  return false;
              }
    }
    public abstract Animal[] multiply(int n);
    
    private boolean isFaster(Animal a) {
        if(this.getSpeed() >a.getSpeed()) {
            return true;
        }else {
        return false;
        }
    }
    
    private boolean isOlder(Animal a) {
        if(this.getAge() >a.getAge()) {
            return true;
        }
        return false;
    }
    @Override
    public String toString() {
        return this.getClass()+ "is " + this.getAge() + " years old, is " +this.getSpeed() +" units fast.";
        
    }
    public final int getAge() {
        return age;
    }

    public final int getSpeed() {
        return speed;
    }



}

I would like to test to see if the variable age exists and also if it is private and final. How would I potentially do this in Junit testing?

What do you mean by `exists`? Do you mean if it has some value? — Arvind Kumar Avinash, Dec 02 '20 at 14:08
I mean it more like to check that class Animal has a variable called age, not necessarily that the value is assigned. — mohelt, Dec 02 '20 at 14:14
Since `age` is declared in the class how could it "not exist"? — Henry, Dec 02 '20 at 14:27
@ArvindKumarAvinash how? You can't delete properties from a class so if the abstract base class has the properties, they're there in all implementing classes whether you want it or not. — Gimby, Dec 02 '20 at 14:49
@Gimby - You are right but OP's question is just about checking if a member exists in a class. — Arvind Kumar Avinash, Dec 02 '20 at 14:51

score 0 · Accepted Answer · answered Dec 02 '20 at 14:36

You can do it as follows:

import static org.junit.jupiter.api.Assertions.assertEquals;

import java.lang.reflect.Field;
import java.util.Arrays;

import org.junit.jupiter.api.Test;

class TestAnimal {
    @Test
    void testAge() {
        Field[] fields = Animal.class.getDeclaredFields();
        assertEquals(true, Arrays.stream(fields).anyMatch(f -> f.getName().equals("age")));
        for (Field f : fields) {
            if (f.getName().equals("age")) {
                assertEquals(0, f.toGenericString().indexOf("private"));
                assertEquals(true, f.toGenericString().contains("final"));
                break;
            }
        }

    }
}

Check the documentation page of Field to learn more about Field#getName and Field#toGenericString.

How to test if a variable exists using JUnit 5?

1 Answers1