← 01 THINKHow does he reason?
A check that never fails is not a check
Every time I build a checker I break it on purpose. A green light alone cannot tell you whether it works or whether it is looking at nothing.
This is the entry retold in plain words. The sentences the author wrote are on the other side of the switch. Nobody wrote the sentences on this page by hand.
I built a device that checks whether colours are easy to see, and ran it. A green light came on.
But one green light cannot tell two things apart.
- The values really are correct
- The checker is looking at nothing
Both show up as a green light.
So I break it on purpose, every time
I deliberately make a colour too faint, then run the checker to see whether it fails when it should fail.
# 1. Set a colour below the threshold, then
node scripts/check-contrast.mjs # failing is correct
# 2. Set a colour that is fine but different from the documented number
node scripts/check-contrast.mjs # this must fail too
The key is that the two failures are different from each other.
The first is a case where things really did become hard to see. The second is a case where they are easy to see but the documentation is lying.
If a site shows its numbers to visitors as they are, it also has to know the moment those numbers stop being true.
I checked the device that keeps the styling order the same way. I deliberately reversed the order, ran it, and it caught it exactly.