The phrase "testing ground" refers to a place or situation where experiments or trials are conducted to assess the effectiveness, success, or potential of something. Full definition
Things like being able to slide down walls and jump from them, and feeling how tight the controls were really made it a good testing ground for new players. (entertainmentbuddha.com)
First, you'll get a kind of testing ground for your own ideas; you'll get to see which branding tactics work and which ones are falling flat. (audiencebloom.com)
The best testing ground for alternative voting methods may be among scientists themselves. (discovermagazine.com)