Instance Variable in JUnit [duplicate]

Question

I have a class that adds elements to a ArrayList (Instance Variable). When I write a test case for the class using Junit, I initialize the class only once. I do the same work in both the test cases.

public class Solution {

    List<String> list = new ArrayList<String>();

    public void modifyList() {
        list.add("A");
        list.add("B");
        list.add("C");
    }
}

SolutionTest.java

public class TestSolution {

    Solution sol = new Solution();

    @Test
    public void testModifyList1() {
        sol.modifyList();
        Assert.assertEquals(3, sol.list.size());
        System.out.println(sol.list);
    }

    @Test
    public void testModifyList2() {
        sol.modifyList();
        Assert.assertEquals(3, sol.list.size());
        System.out.println(sol.list);
    }
}

When I print the list in both the test cases why doesnt the list when printed in the second test case return [A, B, C, A, B, C]. Why does it just return [A, B, C]. My understanding is that, the class is initialized only once, so there is only one copy of the list and it should be modified two times. But, when I print the list it prints only values modified from that test case. Can anyone please explain the behavior ?

When I call the same method on the same object in two different test cases, why isn't the list being updated twice?

Answer 1

The reason for the list not being updated the second time is because of the behavior of Junit. Junit creates an instance of the test class for each test. So, a new object is created for each test case and the list is reinitialized every time.