A trial balloon is a proposal that you mention or an action that you try in order to find out other people's reactions to it, especially if you think they are likely to oppose it.
[mainly US]
They floated the trial balloon of allowing sixteen-year-olds to vote. [+ of]
trial balloon in British English
noun
a tentative action or statement designed to test public opinion on a controversial matter
Compare ballon d'essai
trial balloon in American English
US
1.
pilot balloon
2.
any action, statement, etc. intended to test public opinion on an issue