StudentTestHashtableOpenAdressLinearProbing.java

@Test
public void testTDG() {
  // Configurar aqui!
  final int TESTS_COUNT = 10000;
  final int OPERATIONS_COUNT = 1000;
  final int MAX_SIZE_INCLUSIVE = 31;
  final int MAX_ELEMENT_VALUE = 27; // [0, X).

  Random rand = new Random();
  for (int t = 0; t < TESTS_COUNT; t++) {
    int operations = rand.nextInt(OPERATIONS_COUNT);

    int size = 1 + rand.nextInt(MAX_SIZE_INCLUSIVE);

    HashSet<HashtableElement> jset = new HashSet<>();
    HashtableOpenAddressLinearProbingImpl<HashtableElement> set = new HashtableOpenAddressLinearProbingImpl<>(
        size, HashFunctionClosedAddressMethod.DIVISION);

    for (int i = 0; i < operations; i++) {
      int ch = rand.nextInt(5);

      HashtableElement element = new HashtableElement(rand.nextInt(MAX_ELEMENT_VALUE));

      if (ch == 0) {
        try {
          set.insert(element);
          jset.add(element);
        } catch (HashtableOverflowException ex) {
          assertEquals(size, jset.size());
        }
      } else if (ch == 1) {
        set.remove(element);
        jset.remove(element);
      } else if (ch == 2) {
        if (jset.contains(element)) {
          assertEquals(element, set.search(element));
        } else {
          assertNull(set.search(element));
        }
      } else if (ch == 3) {
        assertEquals(jset.isEmpty(), set.isEmpty());
      } else if (ch == 4) {
        assertEquals(jset.size(), set.size());
      }
    }
  }
}

I think you should try to think more about trick tests than trying to generate randomly tests that will break your code!!!