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Java Unit Testing in Java How to Test Using Before to not repeat yourself

Gary Mclean
Gary Mclean
5,756 Points
Posted by Gary Mclean
Gary Mclean
5,756 Points

use @Before to instantiate a object in JUnit

hi,

the question seems to be easy enough but cant seem to see what i am doing wrong here, it asks me to instantiate a new object and i do that however, it doesnt seem to work.

Any help would be awesome!

P.s the question is I've started the shell for the @Before fixture for these tests. See how the Arrange part is duplicated in both tests, can you help me fix that please?

Use the @Before method to instantiate a new Calculator and use that instance in each method.

com/example/CalculatorTest.java 
package com.example;

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

import static org.junit.Assert.*;

public class CalculatorTest {

private Calculator calculator;

    @Before
    public void setUp() throws Exception {
      Calculator calculator = new Calculator();

    }

    @Test
    public void addingMultipleNumbersProducesResult() throws Exception {
        int answer = calculator.addNumbers(1 ,2, 3);

        assertEquals(6, answer);
    }

    @Test
    public void addingSingleNumberTotalsAppropriately() throws Exception {
        int answer = calculator.addNumbers(1);

        assertEquals(1, answer);
    }
}
com/example/Calculator.java 
package com.example;

public class Calculator {

    public int addNumbers(int... numbers) {
        int total = 0;
        for (int number : numbers) {
            total += number;
        }
        return total;
    }
}

4 Answers

Miguel Canas
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Miguel Canas
Python Development Techdegree Student 11,470 Points
Miguel Canas
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Miguel Canas
Python Development Techdegree Student 11,470 Points

Hi Gary,

You're super close. Here's a hint: consider the scope of the calculator variable in this method:

    @Before
    public void setUp() throws Exception {
      Calculator calculator = new Calculator();
    }

Based on what you've written here, will calculator be accessible outside of the setUp() method? What can you do to make calculator available to other methods in this class?

Hope that helps!

~ Miguel

Gary Mclean
Gary Mclean
5,756 Points
Gary Mclean
Gary Mclean
5,756 Points

Hi, thanks for the tip i made a private field however, it makes the tests fail. any idea why?

" Bummer! 2 out of 2 tests failed. See preview for more details."

"2 FAILURES

addingSingleNumberTotalsAppropriately: null addingMultipleNumbersProducesResult: null

"

Miguel Canas
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.a{fill-rule:evenodd;}techdegree
Miguel Canas
Python Development Techdegree Student 11,470 Points
Miguel Canas
.a{fill-rule:evenodd;}techdegree
Miguel Canas
Python Development Techdegree Student 11,470 Points

OK

    @Before
    public void setUp() throws Exception {
      Calculator calculator = new Calculator();
    }

On this line Calculator calculator = new Calculator() you're declaring the variable in the method's local scope by preceding it with the class name, and not assigning it to the private field.

Gary Mclean
Gary Mclean
5,756 Points
Gary Mclean
Gary Mclean
5,756 Points

Ah, ok, that fixed it. Thanks

Bala Selvam
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Bala Selvam
Python Development Techdegree Student 30,590 Points
Bala Selvam
.a{fill-rule:evenodd;}techdegree
Bala Selvam
Python Development Techdegree Student 30,590 Points

I still don't get it, it is still giving me an error

Austin Gladfelter
Austin Gladfelter
1,801 Points
Austin Gladfelter
Austin Gladfelter
1,801 Points

I'm getting the same thing. Did you ever manage to resolve this?

Christian Dolan
Christian Dolan
1,455 Points
Christian Dolan
Christian Dolan
1,455 Points

Hi im having the same issue as you gary, my tests both fail. How did you end up resolving that?

Christian Dolan
Christian Dolan
1,455 Points

Nevermind I figured it out. I had Calculator calculator = new Calculator();

When it needed to just be calculator = new Calculator();

David Kaiser
David Kaiser
2,079 Points
David Kaiser
David Kaiser
2,079 Points

So my code is below.

It throws the error "Bummer! Please only initialize the Calculator object once in the setUp method that is annotated with @Before." 

package com.example;

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

import static org.junit.Assert.*;

public class CalculatorTest {

  Calculator calculator; 

    @Before
    public void setUp() throws Exception {
      calculator = new Calculator();
    }

    @Test
    public void addingMultipleNumbersProducesResult() throws Exception {
        //Calculator calculator = new Calculator();

        int answer = calculator.addNumbers(1 ,2, 3);

        assertEquals(6, answer);
    }

    @Test
    public void addingSingleNumberTotalsAppropriately() throws Exception {
        //Calculator calculator = new Calculator();

        int answer = calculator.addNumbers(1);

        assertEquals(1, answer);
    }
}

so I only declared the variable once, inside the Setup method, as in the code below, and got this error: There is a compiler error. Please click on preview to view your syntax errors!

A check of the preview shows this: 

./com/example/CalculatorTest.java:19: error: cannot find symbol
        int answer = calculator.addNumbers(1 ,2, 3);
                     ^
  symbol:   variable calculator
  location: class CalculatorTest
./com/example/CalculatorTest.java:28: error: cannot find symbol
        int answer = calculator.addNumbers(1);
                     ^
  symbol:   variable calculator
  location: class CalculatorTest
2 errors

package com.example;

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

import static org.junit.Assert.*;

public class CalculatorTest {

    @Before
    public void setUp() throws Exception {
      Calculator calculator = new Calculator();
    }

    @Test
    public void addingMultipleNumbersProducesResult() throws Exception {
        //Calculator calculator = new Calculator();

        int answer = calculator.addNumbers(1 ,2, 3);

        assertEquals(6, answer);
    }

    @Test
    public void addingSingleNumberTotalsAppropriately() throws Exception {
        //Calculator calculator = new Calculator();

        int answer = calculator.addNumbers(1);

        assertEquals(1, answer);
    }
}