def test_consider_env_plugin_instantiation(self, testdir, monkeypatch):
plugins = PytestPlugins()
testdir.syspathinsert()
testdir.makepyfile(pytest_xy123="class Xy123Plugin: pass")
monkeypatch.setitem(os.environ, 'PYTEST_PLUGINS', 'xy123')
l1 = len(plugins.getplugins())
plugins.consider_env()
l2 = len(plugins.getplugins())
assert l2 == l1 + 1
assert plugins.getplugin('pytest_xy123')
plugins.consider_env()
l3 = len(plugins.getplugins())
assert l2 == l3
