Version control, tests, deploys: the product line

There is a clear line between "a script that worked on my machine once" and "a product". It is not talent. It is three habits, and each one buys you something specific.

1 · Version control buys you *the ability to experiment*. If any change can be undone in one command, you will try bolder things. If it cannot, you will only ever make timid edits.

2 · Tests buy you *the ability to change code you have forgotten*. A test is not there to prove you are right today; it is there so that in six months you can refactor without holding the whole system in your head.

3 · Reproducible deploy buys you *the ability to ship on a bad day*. If deploying requires a particular machine, a particular command history, or a person who remembers the steps, you have a single point of failure that will pick the worst possible moment.

# The whole discipline, in three commands
git add -A && git commit -m "why, not what"   # a checkpoint you can return to

pytest -q                                      # a machine that remembers your intent

# and a deploy that is one command, run from a clean checkout,
# needing no state that lives only in your head:
./deploy.sh                                    # -> same result, any day