self-coded HashTable JUnit Test

I'm working on a self-coded HashTable. And now I stuck in testing the damn thing. This is my test-work so far:

 //Put Test
    Random r = new Random();
    for (int i = 0; i < 1000; i++) {
        int k = r.nextInt(256);
        dummy[i] = k;
        hash.put(i, k);
    }
    assertEquals(1000, hash.size());
    //Key Value Test
    for (int i = 0; i < 1000; i++) {
        assertEquals(dummy[i], hash.get(i));
    }
    //Key Value Test 2
    for (int i = 0; i < 1000; i++) {
        int k = r.nextInt(256);
        if (i % 2 == 0) {
            dummy[i] = k;
            hash.put(i, k);
        }
    }
    for (int i = 0; i < 1000; i++) {
        if (i % 2 != 0) {
            assertEquals(null, hash.get(i));
        }
        if (i % 2 == 0) {
            assertEquals(dummy[i], hash.get(i));
        }
    }
    //Key Value Test 3
    for (int i = 0; i < 1000; i++) {

        if (i % 2 == 0) {
            hash.put(i, null);
        }
        else {
            hash.put(i, 1);
        }
    }
    for (int i = 0; i < 1000; i++) {
        if (i % 2 != 0) {
            assertEquals(1, hash.get(i));

        }
        if (i % 2 == 0) {
            assertEquals(null, hash.get(i));
        }
        //Remove Test
        for (int i = 0; i < 1000; i++) {
            hash.remove(i);

        }

        assertEquals(0, hash.size());
    }
}

Any Ideas how I can test my HashTable better ? Or cleverer ? All my test are functional tests. Maybe a big O-Notation test, but how ?