how to run parallel test in testng.xml
<!DOCTYPE suite SYSTEM "https://testng.org/testng-1.0.dtd" >
<suite name = "Parallel Testing Suite">
<test name = "Parallel Tests" parallel = "classes" thread-count = "2">
<classes>
<class name = "ChromeTest" />
<class name = "FirefoxTest" />
</classes>
</test>
</suite>