If you design things from the start with testing in mind, then your finished system will be both stronger and easier to maintain. One way to accomplish this is to provide a "testing" checkbox (or menu pulldown) in your user interface. Doing so causes a complete design cascade in how you think about development.
It sort of provides you the some comfort level as if you were slipping behind the wheel in a Driver's Training car. It feels like authentic driving but with the added safety that if you forget to step on the brake you actually won't damage anything, as the instructor is watching out for you anyway.
It also allows you the wonderful opportunity to test production interfaces with a development-version of the backing database. Using this practice also promotes looser coupling between components. Of course, make it abundantly clear on the interface (say by changing the global form background color) when the client is in test mode.
This design method does incur some additional logical overhead. Usually you will set a "Testing" Boolean and have places where you evaluate it to set, for example, the database connection strings. This means you also have to provide both the production and development paths and parameters in your config fie.
The saving grace with this approach is that it pretty much clears you from the embarrassment of the all-too-frequent mistake of accidentally copying the development parameters into the production installation. So declare your independence from installation woes: code for testing from the outset and make the development configuration selectable from the interface.