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 ?