Test Everything that could possibly break

What could possibly break? That’s for us to decide.

We can’t test everything.
We can’t test nothing.
So we start with everything that could possibly break.

Testing in XP is a bet. The bet is that value derived from writing the test, is greater than it’s cost to write.

Tests pay us back by telling us:

• when our expectations have been violated.
• when we’ve made a change that broken something that used to work
• by enabling us to make changes with confidence
• and ultimately release something knowing that are core expectations about the system can still be met.