I would put the hose in the drain & turn the water on. Start with a slow stream & keep your eyes & ears on the drain. Also, I would test for only a couple of minutes. Turn off the water & go downstairs to check that the ceiling is still dry. Or have someone else stationed down there. :-). If all is good, then resume the testing.

f this will be an electric dryer, there is an outlet somewhere nearby?

That receptacle should be GFCI.

BleuMax .... "washer dryer combo" refers to a single machine that performs both functions? Choices are few. Most are condenser-drying, which means an exhaust vent is not required ... but you must confirm the installation requirements for the model(s) of consideration. They will require a 240v power supply (not the 120v outlet you show in the photo), unless perhaps there's a heat pump condensing-dryer model available that operates on 120v.

Yes, the dryer would be a condenser dryer. I edited my original post. The model that I am looking at requires a 120v outlet. Per weedmeister's post, I probably need to replace the outlet with a GFCI outlet. The W/D would not be my primary unit, but would make our lives much easier since the new unit would be on the same floor as are primary bedrooms. The main unit is in the basement. This is the model that I am looking at. Condenser W/D units generally receive poor reviews. https://www.ajmadison.com/cgi-bin/ajmadison/GFQ14ESSNWW.html?gclid=Cj0KCQiApY6BBhCsARIsAOI_GjZnbHOhCun5fRwea2_1rhaf6ZRGm3tllTlxkYlS4CtbD56MpTKeLc0aAmeIEALw_wcB