This is a very fgood question and I have an answer. It's apparent that you added a GFCI outlet to your home but you aren't sure that is works. This simple test will put your mind at ease.Look at the face of the GFCI outlet and notice there are two places to plug cords into the outlet. Notice that between these two plug in areas, there are two small buttons. They are labeled test and reset.
To test your ground fault circuit interrupter (GFCI), simply press the test button in. You will hear a snap sound that trips the outlet and cuts power off to the two plugin connections.
This can be checked with a voltage tester or a multimeter to be certain it has turned off the power. You could also plug in a light or device into the outlet and when it quits working when you hit the test button, you'll know the outlets safety mechanism works.
Now that you know it is functioning properly, press the reset button and the outlet should once again be on. Again, you can test this with a tester or by plugging something into the outlet.
As a rule of thumb, I suggest testing the GFCI once a month to ensure the outlet is providing protection for your family. There is no doubt that GFCI outlets save lives. Water and electricity don't mix and that is why these safety devices were developed, to save lives!