This fixes one of the 2 blockers to using pytest instead of Trial (which is not formally-motivated, but sometimes seems like an interesting idea because pytest has seen a lot of developer experience features that Trial hasn't. It would also removes one more coupling to the Twisted framework.) --- The `test_` prefix to this test helper makes it appear as a test to pytest. We *can* set a `__test__ = False` attribute on the test, but it felt cleaner to just rename it (as I also thought it would be a test from that name!). This was previously reported as: https://github.com/element-hq/synapse/issues/18665 --------- Signed-off-by: Olivier 'reivilibre <oliverw@matrix.org>