I need to test my site on an iOS device from a Mac.
Is there a desktop simulator available to do this?
You can use the iOS simulator to do this. You need to enable "Developer Mode" on Safari (Preferences -> Advanced).
Then open the website you want to debug in the iOS simulator. Go back to safari and under Develop you will see the simulator and the tabs open on safari.
If you want to test an actual device, then just plug it into your computer and it should show there too.
That's how I do it.