Test adding a nonexistent unit to cart.

Test adding to cart the same unit. Cart should not change the number of elements. But quantity should be updated if passed.

Test adding to cart by a common user.

Test adding unit to cart not being logged in.

Test adding more items of unit than available.

Log in as a common user.

Log out as a common user.

Test creating order as a common user.

Test order not being logged in.

Test creating order with no units in cart.