tests: add a new test for testing changing or clearing topics test-topic.t is getting bigger and bigger. This patch introduces a new test which includes test for clearing and changing topics. Since the tests are moved to a new file, this patch, removes those tests from test-topic.t also.

obscache: do not check of argument count of wrapped function After talking with the original author of this check, it appears that it never worked properly, since _readmarkers was always wrapped with @util.nogc.

legacy: rename lookup_errors to not be in all caps (flake8 warning) flake8 has a plugin, pep8-naming, which is not installed by default, but is used if available, no extra config required. This plugin checks names of variables, classes, functions and so on against PEP-8, and it complained about this variable: N806 variable in function should be lowercase Since this isn't a module-level constant, but just a helper variable used only in one function, it's fine to just rename it. With this error gone, flake8 output (used plugins: mccabe, naming, pycodestyle, pyflakes) is totally clean.