Installation app on iPhone when device doesn't have enough available storage?

I have some testcases for installation the app on iOS devices but I have no way to figure out the behavior of the AppStore or the iOS (7 and 8) if:

1. Device doesn't have enough storage for downloading file to device
2. Device does have enough storage for downloading file to device but doesn't have enough space for the app to install (because the app size somehow expanded)

Please help me find the way to perform 2 cases here. Thank you for your reading.