This test is not explicit. There is a degeneracy in the possible results concerning z := x.y for
x = 3 | 30
y = 2 | 20

Possible results are: z = 6, 60, 60, 600
The degeneracy lies in the two '60's. In the past, whenever I construct a test involving multiplication, (which is far superior to using addition for this very reason) I always use different prime numbers. This way it is impossible to obtain degenerate results.