what app to use to make sure swap is working

Run some terminal program (e.g. Better Terminal Emulator Pro)In terminal type command "free" with Enter after it. After that you can see total and used physical and swap memory. If Android doesn't use swap you'll see 0 value in swap line, otherwise there will be a nonzero.

The output looks like this (from my linux PC with 4GBs of RAM): [email protected]:~$ free total used free shared buffers cachedMem: 4058604 3900876 157728 0 241136 2778084Swap: 2811332 3432 2807900