Single Test case Run parallel with TestNG Framework

1) Create TestNG class.

package com.software.testing;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;
import org.testng.annotations.BeforeMethod;
import org.testng.annotations.Test;

public class TC1 {
WebDriver driver;

@Test
public void firstTestCase() {
// Printing Id of the thread on using which test method got executed
System.setProperty("webdriver.chrome.driver", "Your Driver Path");
driver = new ChromeDriver();
driver.get("https://www.google.com");
}
}

2) Now Create testng.xml file into your project folder

<suite name="ParallelTestingGoogle" verbose="1" parallel="tests" thread-count="5">
    <test name="1stExecution">
        <classes>
            <class name="com.software.testing.TC1"></class>
        </classes>
    </test>
    <test name="2ndExecution">
        <classes>
            <class name="com.software.testing.TC1" />
        </classes>
    </test>
    <test name="3rdExecution">
        <classes>
            <class name="com.software.testing.TC1" />
        </classes>
    </test>
    <test name="4thExecution">
        <classes>
            <class name="com.software.testing.TC1" />
        </classes>
    </test>
    <test name="5thExecution">
        <classes>
            <class name="com.software.testing.TC1" />
        </classes>
    </test>
</suite>

Note : Don't forget to specify parallel="tests".

When you run your testNg suite it will open five chrome window and run your test case parallel.