_TestingModelBackend was moved with the release of 2.17.0.
~NOTE: ideally we shouldn't be referencing private methods in third party libraries, but it looks like it was for working around something not implemented in Harness. Not sure if we can remove it yet.~
Turns out that the tests pass with the mock removed, so the test harness must implement this now. So we can simply remove the entire mocked function. :D
_TestingModelBackendwas moved with the release of 2.17.0.~NOTE: ideally we shouldn't be referencing private methods in third party libraries, but it looks like it was for working around something not implemented in Harness. Not sure if we can remove it yet.~
Turns out that the tests pass with the mock removed, so the test harness must implement this now. So we can simply remove the entire mocked function. :D