[beefeater]

If you need to make sure every condition is handled, write a test for every condition.

[lmm]

Why? That's both more work and more error-prone than just using a language that will ensure it.

[lgunsch]

If every condition is important to the business, as is implied in this case, it would be very valuable to have tests to cover them.

[lmm]

The business wants to know all conditions are handled appropriately, to a certain level of confidence. Tests are one way of achieving this but by no means the only way.