It looks like a lot of the files from here down are repeats from `plugins/rust/test`. Are you in the middle of moving stuff from there to here? That would be keen: I'd like all the tests to run under a common testrunner before we merge, because we're expecting a lot of refactoring (line-based search, ES) imminently thereafter, and we'll need their support.

That said, longer term, it would be nifty to move the plugin-specific tests (even the clang ones) into the plugins themselves, to establish a pattern for plugins living outside the DXR source tree. (In other words, I liked your initial inclination to put all the rust stuff together.) That should wait until the plugin API refactoring, which will turn plugins into proper Python packages, making such placement of tests easier.