Process lifetime events, like suspend, resume, and being restarted after being terminated by the system from the suspended state, are very important to test with your app. This is because when you're running in a debugger, these events typically don't happen.
Fortunately, Visual Studio provides a menu at debug time to trigger these different events:
Selecting either of the first two will fire the appropriate events, allowing you to set breakpoints in your handlers to debug them.
The third command, Suspend and shutdown, simulates the case where the app is suspended (as if the user switched to another app), and then the system drops the app from memory due to the needs of other apps.
In the debugger, you'll see your suspend events fired, then the app exits and the debugger stops. More importantly, however, is that when you start the debugger again, you'll see the previousExecutionState flag in the activated handler set to terminated. This gives you an easy way to through the startup code path where you'll be rehydrating the app from whatever session state you saved during suspend.
After testing in the debugger, it's a good idea to test the app under real conditions as well. Suspend and resume are easy enough–just switch to other apps. Be sure to leave the app suspended for different lengths of time if you have any kind of timestamp checking in your resuming handler, e.g. code that determines how long it's been since suspend so that it can refresh itself from online content, etc. If you can, try to leave the app suspended for a day or longer, even a week, to really exercise resuming.
To test terminate/restart in a real world scenario, you'll need to basically run a bunch of other memory-hungry apps to force Windows to dump suspended apps out of memory (large games are good for this). You'll make it easier on yourself if you have less memory in the machine to begin with; in fact, to test this condition you could shut down your machine and pull some physical memory (or use an older, less powerful machine for this purpose).
Alternately, you can use a tool that will purposely eat memory, thus triggering terminations. A good list of tools for this purpose can be found on http://beefchunk.com/documentation/sys-programming/malloc/MallocDebug.html.