The discount typed as 100 instead of 10
The invoice goes out for the wrong amount and every step reports success, because arithmetic is not an error.
How it actually happens
Someone types 100 where they meant 10. Or a percentage gets multiplied instead of subtracted. Or a currency conversion runs twice. The math executes perfectly. It is simply the wrong math, and the result travels straight to a customer.
Why nothing catches it
Nothing in a normal stack has an opinion about whether a number is reasonable. There is no alert for an invoice that is ten times too large, because no one ever wrote down what too large means for your business.
What it costs
At best an embarrassed correction. At worst you undercharge for months before anyone notices, and you cannot go back and ask for it.
How we test for it
We build boundary scenarios on invented orders: the maximum discount, the minimum, zero, and the fat finger. The correct output for each is written down before the test runs, so grading is mechanical rather than a matter of opinion.
Find out whether this one applies to you
The fit check is free and written. Four short answers, no call, no files, no credentials. A person reads it and tells you straight whether this is worth checking in your setup.
Request a fit check or call (832) 966-3895
The other patterns
The retry that billed the customer twice · The update that landed on the near twin · The stale update that reversed a correct state · The job marked complete when a step silently failed
All scenarios and amounts on this page are fictional teaching examples, not customer incidents.