is exactly the other way round. It passes -7 to the constructor and checks for 7. This test case should be ok.

    Cube c = new Cube(-7);
    Assert.AreEqual(7, c.GetSide(), "Should be 7");

Kaka's description said to throw ArgumentException if the input was "0". If I didn't have the else it would return 0.

But yeah if you mean that the code terminate after the return anyway, then yeah. Just looks better with the else to me.