Plugins are still loaded when running tests #713

This code has the intention of only loading plugins when not running tests:

However, as far as I can tell, it doesn't function as intended. Plugins are still loaded when running tests. For example, if the https://github.com/simonw/sqlite-migrate plugin is installed on the system, then running pytest fails with errors like this:

    def test_register_commands():
        importlib.reload(cli)
>       assert plugins.get_plugins() == []
E       AssertionError: assert [{'hooks': ['...on': '0.1b0'}] == []
E         
E         Left contains one more item: {'hooks': ['register_commands'], 'name': 'sqlite-migrate', 'version': '0.1b0'}
E         Use -v to get more diff

tests/test_plugins.py:9: AssertionError

As a result, downstream packaging is more difficult, e.g. https://aur.archlinux.org/packages/sqlite-utils#comment-1031481.

The error appears to be because getattr(sys, "_called_from_test", False) is called while loading sqlite_utils.plugins, not at runtime. However, sqlite_utils.plugins is loaded by sqlite_utils.db, which is loaded by sqlite_utils, which is loaded by conftest, so plugins are already loaded before pytest_configure is defined by conftest.