TDD a Java Set - Attempt 5

Set.java

package set;

import java.util.Objects;

public class Set {

    private int size;
    private final int DEFAULT_SIZE = 10;
    private String[] elements = new String[DEFAULT_SIZE];

    public boolean isEmpty() {
        return size == 0;
    }

    public int size() {
        return size;
    }

    public void add(String value) {
        elements[size] = value;
        size++;
    }

    public boolean contains(String value) {
        return indexOf(value) > -1;
    }

    private int indexOf(String value) {
        for (int i = 0; i < size ; i++) {
            if(Objects.equals(elements[i], value)) {
                return i;
            }
        }
        return -1;
    }

    public void remove(String value) {
        for (int i = 0; i < size; i++) {
            if(Objects.equals(elements[i], value)) {
                elements[i] = elements[size];
                size--;
            }
        }
    }
}

SetTest.java

package set;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

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

public class SetTest {

    private Set set;

    @BeforeEach
    void setUp() {
        this.set = new Set();
    }

    @Test
    void is_empty(){
        assertTrue(set.isEmpty());
    }

    @Test
    void empty_set_has_no_size() {
        assertEquals(0, set.size());
    }

    @Test
    void adds_one_element_set_not_empty() {
        set.add("one");
        assertFalse(set.isEmpty());
    }

    @Test
    void adds_one_element_has_size_one() {
        set.add("one");
        assertEquals(1, set.size());
    }

    @Test
    void adds_one_element_contains_element() {
        set.add("one");
        assertTrue(set.contains("one"));
    }

    @Test
    void adds_one_elements_set_not_empty() {
        set.add("one");
        assertFalse(set.isEmpty());
    }

    @Test
    void adds_three_elements_set_not_empty() {
        set.add("one");
        set.add("two");
        set.add("three");
        assertFalse(set.isEmpty());
    }

    @Test
    void adds_three_elements_has_size_three() {
        set.add("one");
        set.add("two");
        set.add("three");
        assertEquals(3, set.size());
    }

    @Test
    void adds_three_elements_contains_three_elements() {
        set.add("one");
        set.add("two");
        set.add("three");
        assertTrue(set.contains("one"));
        assertTrue(set.contains("two"));
        assertTrue(set.contains("three"));
    }

    @Test
    void removes_one_item_set_not_empty() {
        set.add("one");
        set.add("two");
        set.add("three");

        set.remove("two");

        assertFalse(set.isEmpty());
    }

    @Test
    void removes_one_item_reduces_size() {
        set.add("one");
        set.add("two");
        set.add("three");

        set.remove("two");

        assertEquals(2, set.size());
    }
}