WIP implement find_spec in terms of find_module

Related to pytest-dev#1888

_pytest/assertion/rewrite.py

@@ -54,9 +54,20 @@ def __init__(self, config):
         self._register_with_pkg_resources()
         self._must_rewrite = set()
 
+    def invalidate_caches(self):
+        self.modules.clear()
+
     def set_session(self, session):
         self.session = session
 
+    def find_spec(self, fullname, path, target=None):
+        loader = self.find_module(fullname, path)
+        if loader:
+            import importlib.util
+            return importlib.util.spec_from_loader(fullname, loader)
+        else:
+            return None
+
     def find_module(self, name, path=None):
         state = self.config._assertstate
         state.trace("find_module called for: %s" % name)
@@ -210,8 +221,6 @@ def load_module(self, name):
             raise
         return sys.modules[name]
 
-
-
     def is_package(self, name):
         try:
             fd, fn, desc = imp.find_module(name)

_pytest/config.py

@@ -379,6 +379,8 @@ def consider_env(self):
 
     def consider_module(self, mod):
         plugins = getattr(mod, 'pytest_plugins', [])
+        if isinstance(plugins, str):
+            plugins = [plugins]
         self.rewrite_hook.mark_rewrite(*plugins)
         self._import_plugin_specs(plugins)