This test is strictly for a config, so should be moved to TestPALConfig in test_qgspallabeling_base.py. I think it best to have only render-check-based tests for actual output of the labels in this module. Many more config-only tests will be added to TestPALConfig. Since any failure in the TestPALConfig class will have significant effect on any tests in this module, I think it is best to have all config tests in their own class, for faster tracking down of critical failures.

You can probably then add a test for setting setShowingPartialsLabels(bool) to also test the set functionality, then remove any assert test for the setting in this class (in two other tests), since the render check will be enough verify the test.