Inside your Rapise test's user functions file (mytest.user.js), add the following:

function CloseBrowser()
{
 switch (g_browser_library)
 {
  case "Internet Explorer HTML":
   
Global.DoLaunch('Taskkill /IM iexplore.exe');
   break;

  case "Firefox HTML":
   Global.DoLaunch('Taskkill /IM firefox.exe');
   break;

  case "Chrome HTML":
   
Global.DoLaunch('Taskkill /IM chrome.exe');
   break;   
 }
}

Then just call the CloseBrowser() function from your main test script.

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Alternatively, you can use the following:

function KillBrowser()
{
 switch (g_browser_library)
 {
  case "Internet Explorer HTML":
   Global.DoKillByName('iexplore.exe');
   break;
  case "Firefox HTML":
   Global.DoKillByName('firefox.exe');
   break;
  case "Chrome HTML":
   Global.DoKillByName('chrome.exe');
   break;   
 }
}

Then just call the KillBrowser() function from your main test script.