Selenium WebDriver C# test case is inadvertently running twice

I'm using VS 2015 community. My Selenium C# test case always runs twice. The Test Case Explorer window shows 1 test case was run but the pass result shows two of the same test cases were executed. What is wrong with my test or framework? I have created a Test File with testcase (NunitDemo.cs) under my project.

I attached a screenshot to my Solutions Explorer window as well.

using NUnit.Framework;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using OpenQA.Selenium;
using OpenQA.Selenium.Firefox;


namespace DemoNunit
{

    [TestFixture]
    public class NunitDemo
    {
        private IWebDriver driver;

        [Test]
        public void tc_newAccount()
        {
            //open browser and navigate to aut
            driver = new FirefoxDriver();
            driver.Navigate().GoToUrl("http://www.trainingrite.net");

            //click on signup button
            driver.FindElement(By.CssSelector("input.submitbtn")).Click();


            //enter firstname,  lastname, email, password
            driver.FindElement(By.Id("ctl00_MainContent_txtFirstName")).Clear();
            driver.FindElement(By.Id("ctl00_MainContent_txtFirstName")).SendKeys("Ren");
            driver.FindElement(By.Id("ctl00_MainContent_txtLastName")).Clear();
            driver.FindElement(By.Id("ctl00_MainContent_txtLastName")).SendKeys("G");
            driver.FindElement(By.Id("ctl00_MainContent_txtEmail")).Clear();
            driver.FindElement(By.Id("ctl00_MainContent_txtEmail")).SendKeys("[email protected]");
            driver.FindElement(By.Id("ctl00_MainContent_txtPassword")).Clear();
            driver.FindElement(By.Id("ctl00_MainContent_txtPassword")).SendKeys("12345");
            driver.FindElement(By.Id("ctl00_MainContent_txtVerifyPassword")).Clear();
            driver.FindElement(By.Id("ctl00_MainContent_txtVerifyPassword")).SendKeys("12345");
            driver.FindElement(By.Id("ctl00_MainContent_txtHomePhone")).Clear();
            driver.FindElement(By.Id("ctl00_MainContent_txtHomePhone")).SendKeys("951-265-1234");
            driver.FindElement(By.Id("ctl00_MainContent_txtCellPhone")).Clear();
            driver.FindElement(By.Id("ctl00_MainContent_txtCellPhone")).SendKeys("760-855-1234");
            driver.FindElement(By.Id("ctl00_MainContent_txtInstructions")).Clear();
            driver.FindElement(By.Id("ctl00_MainContent_txtInstructions")).SendKeys("Running first selenium automation scripts in C#!");

            //click on submit button
            driver.FindElement(By.Id("ctl00_MainContent_btnSubmit")).Click();


            //verify new customer is added successfully
            Assert.AreEqual("Customer information added successfully",  driver.FindElement(By.Id("ctl00_MainContent_lblTransactionResult")).Text);

        }
    }
}