Junit BeforeAll or BeforeEach - when to initialise class under test if state does not change between tests?

Question

In my following example I am unsure if I should use BeforeEach or BeforeAll - Note the class under test Calculator does not change state etc between tests so I assumed making it static and using BeforeEach is more efficient?

public class CalculatorShould {

    private static Calculator calculator;

    @BeforeAll
    static void setUp() {
        calculator= new Calculator();
    }

    @Test
    void calculatePriceForTwo() {

        // act
        Double price = calculator.calculatePrice(2);

        // assert
        assertEquals(10, price);
    }

    @Test
    void calculatePriceForFour() {

        // act
        Double price = calculator.calculatePrice(4);

        // assert
        assertEquals(20, price);
    }
}

armandino · Accepted Answer · 2023-02-10T00:05:59.210

2

I think in your example you don't need either BeforeAll or BeforeEach.

Instead, it's simpler (less code is good) to just declare:

public class CalculatorShould {

    private Calculator calculator = new Calculator();

    // test methods unchanged...
}

JUnit will provide you with a brand new instance of the Calculator before each test method is run:

In order to allow individual test methods to be executed in isolation and to avoid unexpected side effects due to mutable test instance state, JUnit creates a new instance of each test class before executing each test method (see Test Classes and Methods). This "per-method" test instance lifecycle is the default behavior in JUnit Jupiter and is analogous to all previous versions of JUnit.

Source: https://junit.org/junit5/docs/current/user-guide/#writing-tests-test-instance-lifecycle

edited Feb 10 '23 at 00:05

answered Feb 09 '23 at 23:54

armandino

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do you mean declare it in each test? before if I declare it outside each test method then each test cant access as its outside the scope? – java12399900 Feb 09 '23 at 23:57
Not in each test, but as a field. I updated the sample. – armandino Feb 10 '23 at 00:01
Thanks, but how does this give a new instance before each test? Is each test not just reusing the same calculator object? – java12399900 Feb 10 '23 at 00:03
It will only reuse the same instance if you declare the `Calculator` as a `static` field. If it's not `static`, a new instance will be created. I added a link to the documentation that has more details. – armandino Feb 10 '23 at 00:07
appreciate it, answer accepted! – java12399900 Feb 10 '23 at 00:31

Junit BeforeAll or BeforeEach - when to initialise class under test if state does not change between tests?

1 Answers1