[est31]

I know a little about two of the big open source Rust projects, Servo and the Rust compiler.

For integration tests, both the Rust compiler as well as the Servo web engine have written their own test runners with an accompanying set of tools. This allows the test format to be as flexible as the target domain of the program. In fact, servo can just simply use the cross-browser wpt [1] test suite.

As for avoiding to initialize heavy objects, I only know about the Rust compiler's test runner initializing the entire compiler every time from zero for every single test file. The result is a quite long testing-time. Suggestions by me to use a shared driver were rejected by them because one test might affect the other one.

But in theory you could write your own custom test runner that has as much shared state as possible. You might also want to check out cucumber-rust [2] which I think allows for some way of sharing. You could also just group smaller tests into a small set of bigger tests where each group of tests shares some resource.

[1]: https://github.com/web-platform-tests/wpt [2]: https://github.com/bbqsrc/cucumber-rust