1. To subject something to a critical evaluation of its quality or ability within some particular place or thing. A noun or pronoun is used between "test" and "in." We'll need to test the device in saltwater to be sure it doesn't corrode. We have tested the product very vigorously in our lab.

2. To subject someone to a critical evaluation of their knowledge or ability in a particular subject, field, or task. A noun or pronoun is used between "test" and "in." The written exam will test you in your knowledge of the various driving laws, while the behind-the-wheel exam will test you in your ability to apply them on the road. They test all potential teachers in their Japanese to make sure they will not struggle to adapt once they arrive in Tokyo.