Thank you for your answers.
It would be for simple PHP/MySQL MODx websites, so that I have a temporary solution whilst testing a VPS.
The idea is not being under pressure whilst installing/configuring/testing a VPS like VULTR, DigitalOcean or UpCloud ones.
I found these ones allowing short duration:
Both seem using cPanel, which I dislike.
My current host, Yellis.net has currently 4-month plans because it will end its activity at the end of 2016. I like its reliability, its panel and the support is competent.
For those speaking French, I found out that Gandi.net, who is well known in France, has a solution named "Simple Hosting", https://www.gandi.net/hebergement/simple
, which is cloud based, has 10 free days and seem allowing billing per month. It seems being in the middle of a shared hosting and a VPS (dedicated ressources like a VPS, but I assume with an admin panel like a shared hosting).