First point is- showing multiple popups is not desirable in terms of usability.
But you can achieve it by using multiple popup names
var newwindow;
function createPop(url, name)
{
newwindow=window.open(url,name,'width=560,height=340,toolbar=0,menubar=0,location=0');
if (window.focus) {newwindow.focus()}
}
Better approach will be showing both in a single page in two different iFrames or Divs.
Update:
So I will suggest to create a new tab in the test.aspx page to show the report, instead of replacing the image content and placing the pdf.