how to write a junit test case for this class

UPDATED

I am trying to write a test case for the following code using Mockito and Junit.. May I know how should i write it. As i am new to this language i don't have much idea about it. I have coded test case for patientDao(which is passing) class but i dont know how to do it for SaveServlet

Apologizing for the mistakes in the code.

Note* - I am not using any frameworks.

Save Servler.java

   package com.consentServlets;

    import java.io.IOException;
    import java.io.PrintWriter;

    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    @WebServlet("/SavePolicy")
    public class SavePolicy extends HttpServlet {
        protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            response.setContentType("text/html");
            PrintWriter out=response.getWriter();
            //Getting the attributes from the UI
            String policy_Name = request.getParameter("policy_name");
            String organization_Name = request.getParameter("orgid");
            String start_Date=request.getParameter("sop");
            String end_Date = request.getParameter("eop");
            //Setting the objects to insert the achieved attributes to corresponding the columns of the table
            policy savePolicy = new policy();
            savePolicy.setPolicyName(policy_Name);
            savePolicy.setOrgName(organization_Name);
            savePolicy.setStartDate(start_Date);
            savePolicy.setEndDate(end_Date);


            out.print(" <link rel=\"stylesheet\" href=\"https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.css\">");
            //calling the save function from the patientDao class to execute the query
            DataConnection ds = new DataConnection();
            int status=new policyDao(ds).add(savePolicy);
            if(status>0){
                out.print("<p>Policy added successfully!</p>");
                request.getRequestDispatcher("manage_policy.html").include(request, response);
            }else{
                out.println("Sorry! failed");
            }

            out.close();
        }

    }

PatientDao.java

package com.consentServlets;
import java.sql.Connection;

import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List; 

import java.sql.SQLException;
import javax.sql.DataSource;


public class patientDao {
    public DataConnection ds;
    public patientDao(DataConnection ds) {
        this.ds = ds;
    }
    public int save(patient addPatient){  
        int status = 0;  
        //Inserting patient details from UI to Database
        try{                            
            Connection con = ds.getConnection();  
            System.out.println(addPatient.getLastName());
            PreparedStatement ps = con.prepareStatement(  
                    "insert into patient(last_name,first_name,gender,age,dob) values (?,?,?,?,?)");  
            ps.setString(1,addPatient.getLastName());  
            ps.setString(2,addPatient.getFirstName());  
            ps.setString(3,addPatient.getGender());  
            ps.setString(4,addPatient.getAge());
            ps.setString(5,addPatient.getDoB());

            status = ps.executeUpdate();
            System.out.println(status);
            con.close();  
        }catch (SQLException e) {
            throw  new RuntimeException(e);}


        return status;  
    }  

    // Fetching all the records from table
    public  List<patient> getAllPatients(){  
        List<patient> list = new ArrayList<patient>();  

        try{  
            Connection con = ds.getConnection();  
            PreparedStatement ps = con.prepareStatement("select * from patient");  
            ResultSet rs = ps.executeQuery();  
            while(rs.next()){  
                patient getAllPatients=new patient();  
                getAllPatients.setId(rs.getInt(1));  
                getAllPatients.setFirstName(rs.getString(3));  
                getAllPatients.setLastName(rs.getString(2));  
                getAllPatients.setGender(rs.getString(4));  
                getAllPatients.setAge(rs.getString(5));
                getAllPatients.setDoB(rs.getString(6));   
                list.add(getAllPatients);  
            }  
            con.close();  
        }catch(Exception e){e.printStackTrace();}  

        return list;  
    }  
}  

patient.java

package com.consentServlets;
import java.util.List;
//creating objects for patient class which will help to store the patient details
public class patient {  
    private int id;  
    private String first_Name,last_Name,gender,age,dob;  
    public int getId() {  
        return id;  
    }  
    public void setId(int id) {  
        this.id = id;  
    }  
    public String getFirstName() {   
        return first_Name;  
    }  
    public void setFirstName(String first_Name) {  
        this.first_Name = first_Name;  
    }  
    public String getLastName() {  
        return last_Name;  
    }  
    public void setLastName(String last_Name) {  
        this.last_Name = last_Name;  
    }  
    public String getGender() {  
        return gender;  
    }  
    public void setGender(String Gender) {  
        this.gender = Gender;  
    }  
    public String getAge() {  
        return age;  
    }  
    public void setAge(String Age) {  
        this.age = Age;  
    }  
    public String getDoB() {  
        return dob;  
    }  
    public void setDoB(String DOB) {  
        this.dob = DOB;  
    }
}