Unit tests in java : Im making an application in android studio. And for this project i have to make multiple unit tests. But i have no idea what i can unit test this application. Im really struggeling with unit testing so i would appreciate if someone could help me, or come up with some unit tests i can implement in my project. Its an app with a listview that retrieves data from a webservice.

Code: 
            
     public class MainActivity extends AppCompatActivity {

    ListView listView;
    ArrayAdapter<String> adapter;
    String[] data;
    String[] waarde;
    String[] hoog;
    String[] laag;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        listView = findViewById(R.id.listview);

        StrictMode.setThreadPolicy(new StrictMode.ThreadPolicy.Builder().permitNetwork().build());

        getData();

        listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            Intent intent = new Intent(MainActivity.this, Showdata.class);
            intent.putExtra("teeltbed", listView.getItemAtPosition(position).toString());
            startActivity(intent);
            }
        });

    }

    private void getData()
    {
        String getData = null;
        String dbResult = "empty";
        dbConnect database = new dbConnect(this);

        try{
            String query = "SELECT * FROM Lamp";
            getData = "?query=" + URLEncoder.encode(query, "UTF-8");
            //data += "&username=" + URLEncoder.encode(userName, "UTF-8");
            String link = "http://10.247.240.53/kas/lampen.php";
            dbResult = database.execute(link).get();
        }
        catch (Exception e){

        }

        try{
            JSONObject jsonObject = new JSONObject(dbResult);
            JSONArray array = jsonObject.getJSONArray("Lamp");
            waarde = new String[array.length()];
            data = new String[array.length()];
            hoog = new String[array.length()];
            laag = new String[array.length()];
            for (int i = 0; i < array.length(); i++)
            {
                jsonObject = array.getJSONObject(i);
                data[i] = jsonObject.getString("teeltbed");
                waarde[i] = "A: " + jsonObject.getString("waarde") + " %";
                hoog[i] = "H: " + jsonObject.getString("hoog") + " W/m2";
                laag[i] = "L: " + jsonObject.getString("laag") + " W/m2";

            }

            listView.setAdapter(new dataListAdapter(data, waarde, hoog, laag));
        }

        catch (Exception e)
        {
            e.printStackTrace();
        }
    }

    class dataListAdapter extends BaseAdapter{
        String[] data, waarde;

        dataListAdapter(){
            data = null;
            waarde = null;
        }

        public dataListAdapter(String[] sdata, String[]swaarde, String[]shoog, String[]slaag)
        {
            data = sdata;
            waarde = swaarde;
            hoog = shoog;
            laag = slaag;

        }

        public int getCount()
        {
            return data.length;
        }

        public Object getItem(int arg0) {
            // TODO Auto-generated method stub
            return null;
        }

        public long getItemId(int position) {
            // TODO Auto-generated method stub
            return position;
        }

        public View getView (int position, View convertView, ViewGroup parent)
        {
            LayoutInflater inflater = getLayoutInflater();
            View row;
            row = inflater.inflate(R.layout.layout_list, parent, false);
            TextView t1, t2, t3, t4;
            t1 = (TextView) row.findViewById(R.id.list_item);
            t2 = (TextView) row.findViewById(R.id.list_item2);
            t3 = (TextView) row.findViewById(R.id.list_item3);
            t4 = (TextView) row.findViewById(R.id.list_item4);
            t1.setText(data[position]);
            t2.setText(waarde[position]);
            t3.setText(hoog[position]);
            t4.setText(laag[position]);
            return (row);
        }
    }

    class Sproeier
    {
     public int TeeltBed;
     public String Stand;
     public double Actueel;
     public double Hoog;
     public double Laag;

     public void Sproeier()
     {
         int teeltbed;
         double hoog;
         double laag;
     }
    }

    class Lamp {

    }

    public static class ScadaWebservice
    {

    }

    class Kas
    {

        public void kas()
        {

        }
    }
}