ChromeExtensionTest.java

import org.openqa.selenium.Cookie;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.chrome.ChromeDriver;
import org.openqa.selenium.chrome.ChromeOptions;
import org.openqa.selenium.remote.DesiredCapabilities;
import org.openqa.selenium.remote.RemoteWebDriver;

import java.io.File;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Calendar;
import java.util.Date;

public class ChromeExtensionTest {

    public static void main(String[] args) {

        ChromeOptions options = new ChromeOptions();
        options.addExtensions(new File("/path/to/crx/file"));
        WebDriver driver = new ChromeDriver(options);

        driver.get("https://google.co.in");

        try {
            Thread.sleep(10000);
        } catch (Exception e) {
            e.printStackTrace();
        }

        driver.quit();
    }
}