Here ground refers to 0V i.e between +15 and -15. Now if you practically check the output of 741 with both inputs connected to 0V the output is at +2.5V. And even in simulation the output shows 2.439V. This is due to very very very small offset present between two inputs.
If ground refers to Vee then there would be no bias current for the input stages, so it would not really be a test.
Here if you connect both inputs to -Vee the output swings to +Vcc
and if both inputs are conneted to Vcc the output swings to -Vee. So this is a test.
Just check this funny behaviour on breadboard