add test case and fix typo

ddtrace/internal/module.py

@@ -324,7 +324,7 @@ def find_module(self, fullname, path=None):
                     loader = _ImportHookChainedLoader(loader)
 
                 if PY2:
-                    # With Python 2 we don't get all the finder invoked, so we
+                    # With Python 2 we don't get all the finders invoked, so we
                     # make sure we register all the callbacks at the earliest
                     # opportunity.
                     for finder in sys.meta_path:

tests/internal/test_module.py

@@ -310,3 +310,20 @@ class Bob(BaseCollector):
 
     Bob.uninstall()
     Alice.uninstall()
+
+
+def test_module_watchdog_dict_shallow_copy():
+    # Save original reference to sys.modules
+    original_sys_modules = sys.modules
+
+    ModuleWatchdog.install()
+
+    # Ensure that we have replaced sys.modules
+    assert original_sys_modules is not sys.modules
+
+    # Make a shallow copy of both using the dict constructor
+    original_modules = set(dict(original_sys_modules).keys())
+    new_modules = set(dict(sys.modules).keys())
+
+    # Ensure that they match
+    assert original_modules == new_modules