If you're paid per hour and your client want you to take the less possible time. It's stupid; I agree. You can try argue with him/her about the importance of it, but in the end, it's their money so it's their choice.
It irks me when clients tell me how I should do the thing they're paying me to do. It seems counterproductive and is insulting.
It's a little bit like if you eat at a restaurant and you've got 20$. The cook could tell you there's something really good and way better at 50$.. but if you're happy with something less good at 15$, well, it's your body and your money. (I know that development is way different and in the long term tests will save money, but depending of the project, it's not always the case.)