This isn't much of a test, is it? You need to actually check that the constructor works correctly, presumably by checking if the rectangle's points contain the three input points.

I suggest you use our randomized testing framework. Create a subclass of `cvtest::BaseTest`, and override its methods:

* in `prepare_test_case`, generate 3 random points (with AB orthogonal to BC, of course);
* in `run_func`, create the `RotatedRect`;
* in `validate_test_results`, check that the 3 original points are amongst the rect's points.

See the existing tests for examples.