Testing, or checking? It matters which.
A test is something you do to find out whether somebody will fail. A check is something you do to find out whether something is still there. Almost none of this is testing.
A rule that never moves only has to be checked once. A rule that moves - sometimes, in certain moods, when you are tired, when somebody is visiting - has to be checked every single time. And every rule in every house moves sometimes. You are a person, not a policy.
What it costs is not the argument. It is the running total: forty small negotiations before ten in the morning - the coat, the seat in the car, which cup, which stair to stand on, whether that counts as one biscuit or two, and the exact status of a promise made on Sunday. Each one requiring you to decide, hold, explain, and then hold again.
Which is why it produces a particular kind of anger. Not the hot sort. The flat, tired sort that arrives over something absurdly small, usually a cup, and then feels ridiculous afterwards.
What is in it:

• Which of your rules actually move, honestly - including the ones that move on holiday, and the ones the other adult holds differently
• Why explaining the reason hands them the material for the next four minutes
• Why winning it thoroughly guarantees a rematch
• Six words, then nothing - why the repetition is the technique and not the wording
• Leaving the room, which is not ignoring them: you cannot negotiate with somebody who has gone to hang the washing out
• Two adults and one answer, and why this is where most of the difficulty actually lives
• The particular indignity of losing an argument to somebody who believes the moon follows the car

The aim is not a child who accepts things. It is fewer negotiations, and shorter ones.
Four rules held quietly beat forty held anxiously.
"Say it once. Then hang the washing out."
For the parent, not the child. Sixty-four pages, small enough for a coat pocket.
This book supports everyday emotional awareness. It is not a screening tool and it is not a substitute for professional guidance.
From the Little Signals world: quiet stories and tools that help small humans notice their signals and find their way back to steady. No quick fixes. No hype. Regulation before optimisation.