How to start unit testing for windows forms?

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testing

C#5.0

I have a block of code which has a security context.
Now my question is how do i go about unit testing this? This is a windows form. Written in C#. I have created a unit test project. I want to know what classes should i include and how to do them. Have used datagridview to display the items

private void btnsearch_Click(object sender, EventArgs e)
        {
            string lastname=null;
            refreshgrid();
            Regex pattern = new Regex("^[a-zA-Z'-]{1,30}$");
            if (String.IsNullOrEmpty(txtlname.Text)) //Checks if the textbox is empty or not
            {
                toolStripStatusLabel1.Text= "Last name Required";
            }
            else if (pattern.IsMatch(txtlname.Text)) //Regex pattern matching is done here
            {
                lastname = txtlname.Text.ToUpper().Trim(); //Trims the before and after spaces
                fetchPatientDetails(lastname);
            }
            else
            {
                toolStripStatusLabel1.Text = "Invalid Input";
            }
        }

private void GridOperations(object sender, DataGridViewCellEventArgs e)
        {
            int rowindex = e.RowIndex;
            DataGridViewRow row = ((DataGridView)sender).Rows[rowindex];
            string id = row.Cells[0].Value.ToString();
            switch (((DataGridView)sender).Name)
            {
                case "dgvpatient":
                    hidereaction();
                    hideallergy();
                    lblencounter.Show();
                    string patientid = row.Cells[0].Value.ToString();
                    displayDetails(sender, id, 1, 2180508);
                    break;

                case "dgvencounter":
                    hidereaction();
                    lblallergy.Show();
                    displayDetails(sender, id, 2, 2180509);
                    break;

                case "dgvallergy":
                    lblreaction.Show();
                    displayDetails(sender, id, 3, 2180510);
                    break;
            }
        }

What I have tried:

I have no idea how to proceed.
Hence i have not tried anything