creating worst-case scenario test environment for wireless
You'll find that microwave ovens, aluminum foil, metal garbage cans etc aren't really reliable attenuators. 

What you need is a channel model that tells you how much your signal will be attenuated after 1km, but also how bad your multipath will be like, together with a signal model that tells you what effect that has in your reception.

I don't know the devices you're referring to, but usually I'd expect an antenna connector to be present in anything that I'd expect to work over such distances, so instead of an antenna, connect your transmitter and receiver with coax cable and attenuators to emulate the attenuation. It's much harder to emulate the multipath environment and temporal effects like fading, but with your signal model you might be able to calculate an attenuation that would be "just as bad" as an actual multipath channel.