test a void method using JUnit

Question

I'm trying to test a void method using JUnit in NetBeans, my method is changing the value of a double variable and then print the new variable's valur into a TextField, this is my method :

private void calcul(){

        if(operateur.equals("+")){
            chiffre1 = chiffre1 + Double.valueOf(ecran.getText()).doubleValue();
            ecran.setText(String.valueOf(chiffre1));
        }
        if(operateur.equals("-")){
            chiffre1 = chiffre1 - Double.valueOf(ecran.getText()).doubleValue();
            ecran.setText(String.valueOf(chiffre1));
        }          
        if(operateur.equals("*")){
            chiffre1 = chiffre1 * Double.valueOf(ecran.getText()).doubleValue();
            ecran.setText(String.valueOf(chiffre1));
        }     
        if(operateur.equals("/")){
            try{
                chiffre1 = chiffre1 / Double.valueOf(ecran.getText()).doubleValue();
                ecran.setText(String.valueOf(chiffre1));
            } catch(DivisionSurZeroException e) {
                ecran.setText("0");
            }
        }
    }

I Googled about how to test void method but all I can find is void methods that changes the size of a collection.

So please can you give me some idea to start with ? I really don't know what to start with.

Answer 1

You have to create new entity of tested class and after that call tested function. Later on assert that values have changed as you wanted to.

TestedClass tested = new TestedClass();
tested.calcul();

assertEquals("val", tested.getVal());

However, in your example method is private. To test it you may try to use PowerMock .

Answer 2

1. you could split your method into several smaller methods - one for each operator - and test them independently.

2. testing void methods is not too different from testing methods with return values:

   1. set up the preconditions
   2. run your method
   3. check the postconditions

in your case:

yourClass.setOperateur("+");
yourClass.setChiffre1(5);
yourClass.setEcran("7");

yourClass.calcul();

assertEquals("12", yourClass.getEcran());