This is Grinder's test script. I edited on basic script for my needs. You can see normal basic script on nGrinder program.

nGrinder_test.groovy

import static net.grinder.script.Grinder.grinder
import static org.junit.Assert.*
import static org.hamcrest.Matchers.*
import net.grinder.plugin.http.HTTPRequest
import net.grinder.plugin.http.HTTPPluginControl
import net.grinder.script.GTest
import net.grinder.script.Grinder
import net.grinder.scriptengine.groovy.junit.GrinderRunner
import net.grinder.scriptengine.groovy.junit.annotation.BeforeProcess
import net.grinder.scriptengine.groovy.junit.annotation.BeforeThread
// import static net.grinder.util.GrinderUtils.* // You can use this if you're using nGrinder after 3.2.3
import org.junit.Before
import org.junit.BeforeClass
import org.junit.Test
import org.junit.runner.RunWith

import java.util.Date
import java.util.List
import java.util.ArrayList

import HTTPClient.Cookie
import HTTPClient.CookieModule
import HTTPClient.HTTPResponse
import HTTPClient.NVPair


/**
 * A simple example using the HTTP plugin that shows the retrieval of a
 * single page via HTTP. 
 * 
 * This script is automatically generated by ngrinder.
 * 
 * @author admin
 */
@RunWith(GrinderRunner)
class TestRunner {

	public static GTest test
	public static HTTPRequest request
	public static NVPair[] headers = []
	public static NVPair[] params = []
	public static Cookie[] cookies = []
	public static String userValue
		
	//method for making random value 
	public static String setRandomUserValue(String before="", int size){
		def generator = { String alphabet, int n ->
		  new Random().with {
			(1..n).collect { alphabet[ nextInt( alphabet.length() ) ] }.join()
		  }
		}

		return generator( (('A'..'Z')+('0'..'9')).join(), size )
	}

	@BeforeProcess
	public static void beforeProcess() {
		//HTTPPluginControl.getConnectionDefaults().timeout = 6000
		
		//set timeout value. if you need more wait time from your system, set time here. 
		HTTPPluginControl.getConnectionDefaults().setTimeout(30000)
		test = new GTest(1, "aaa.yoursytem.com")
		request = new HTTPRequest()
		// Set header datas
		List<NVPair> headerList = new ArrayList<NVPair>()
		
		//set request value for Header
		headerList.add(new NVPair("Content-Type", "application/x-www-form-urlencoded"))
		//headerList.add(new NVPair("token", "aaaaaa"))
		headers = headerList.toArray()
		
		// Set param datas
		List<NVPair> paramList = new ArrayList<NVPair>()
		//paramList.add(new NVPair("aKey", setRandomUserValue("",15)))
		//paramList.add(new NVPair("bKey", setRandomUserValue("TEST",8)))
		params = paramList.toArray()
		grinder.logger.info("before process.");
	}

	@BeforeThread 
	public void beforeThread() {
		test.record(this, "test")
		grinder.statistics.delayReports=true;
		grinder.logger.info("before thread.");
	}
	
	@Before
	public void before() {
		request.setHeaders(headers)
		cookies.each { CookieModule.addCookie(it, HTTPPluginControl.getThreadHTTPClientContext()) }
		grinder.logger.info("before. init headers and cookies");
	}

	@Test
	public void test(){
		HTTPResponse result = request.GET("https://aaa.yoursytem.com/bbb", params)

		if (result.statusCode == 301 || result.statusCode == 302) {
			grinder.logger.warn("Warning. The response may not be correct. The response code was {}.", result.statusCode); 
		} else {
			assertThat(result.statusCode, is(200));
		}
	}
}