https://phys.org/news/2018-06-einstein-theory-gravity-extreme-conditions.html

Einstein's theory has passed all tests in laboratories and elsewhere in our solar system. But scientists know that quantum mechanics behaves differently, so Einstein's theory has to break somewhere. Does this principle also hold for objects with extreme gravity?

The answer is "yes," according to an international team of astronomers, including one from the University of Wisconsin-Milwaukee. They have tested the question with the help of three stars orbiting each other in a natural "laboratory" about 4,200 light years from Earth.