It basically needs to cover all cases. In this case 2^4 cases in increasing order (ramp) in order to test the DUT for all possible inputs.
Like:
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
.
.
.
1111
It basically needs to cover all cases. In this case 2^4 cases in increasing order (ramp) in order to test the DUT for all possible inputs.
Like:
0000
0001
0010
0011
0100
0101
0110
0111
1000
1001
.
.
.
1111