Here you go.

Refactoring Bob changed the line
if i !> x do to
if i < x do. Looked fine
When he ran a use case or two.

He checked the change in as “all tested,
Compiled and ready to ship!”
Though QA complained and protested,
The deadlines weren’t subject to slip.

The system looked fine throughout beta
And Wired said its future was bright.
But then, with the userbase greater*,
A cluster of faults came to light.

The bug reports soon flooded in;
The system phoned home in distress.
Support found their patience wear thin,
Till management queried “the mess”.

Retesting to track down the glitch
Was run, and it soon stood revealed:
The use case (i = x) which
Inadequate tests had concealed.

A fix was soon made and compiled
And users, their systems now patched,
Then found their results reconciled.
And thus was this code bug despatched.

—-
* An evil rhyme, but it had to be done