You can use --dist=loadscope to group all the tests in the same test class. Here is the doc from pytest-xdist on pypi
By default, the -n option will send pending tests to any worker that is available, without any guaranteed order, but you can control this with these options:
--dist=loadscope: tests will be grouped by module for test functions and by class for test methods, then each group will be sent to an available worker, guaranteeing that all tests in a group run in the same process. This can be useful if you have expensive module-level or class-level fixtures. Currently the groupings can’t be customized, with grouping by class takes priority over grouping by module. This feature was added in version 1.19.
--dist=loadfile: tests will be grouped by file name, and then will be sent to an available worker, guaranteeing that all tests in a group run in the same worker. This feature was added in version 1.21.