It would be nice if xUnit supported passing a simple expression argument to the runners to filter down the set of tests to execute. Today, xUnit only supports passing -trait, -notrait, -method, etc arguments that have preset boolean logic applied. This means that certain test combinations are not expressible, with the only alternatives being performing multiple runs, or listing each test method individually on the command line. For those of us with very large test bases, neither alternative is very practical.

dotnet vstest has a similar --TestCaseFilter option that allows passing an expression, but that runner is missing many other nice features/perfomance of xUnit's runners, so it would be great if xUnit could be enhanced in this way.