Backport fix for test isolation from Python 3.8/3.7. Closes python#61

Author: warsaw

importlib_resources/docs/changelog.rst

@@ -2,6 +2,10 @@
  importlib_resources NEWS
 ==========================
 
+1.0 (2018-XX-XX)
+================
+* Backport fix for test isolation from Python 3.8/3.7.  Closes #61
+
 0.8 (2018-05-17)
 ================
 * Strip ``importlib_resources.__version__``.  Closes #56

importlib_resources/tests/util.py

@@ -10,6 +10,30 @@
 from .._compat import ABC, Path, PurePath, FileNotFoundError
 from ..abc import ResourceReader
 
+try:
+    from test.support import modules_setup, modules_cleanup
+except ImportError:
+    # Python 2.7.
+    def modules_setup():
+        return sys.modules.copy(),
+
+    def modules_cleanup(oldmodules):
+        # Encoders/decoders are registered permanently within the internal
+        # codec cache. If we destroy the corresponding modules their
+        # globals will be set to None which will trip up the cached functions.
+        encodings = [(k, v) for k, v in sys.modules.items()
+                     if k.startswith('encodings.')]
+        sys.modules.clear()
+        sys.modules.update(encodings)
+        # XXX: This kind of problem can affect more than just encodings. In
+        # particular extension modules (such as _ssl) don't cope with reloading
+        # properly.  Really, test modules should be cleaning out the test
+        # specific modules they know they added (ala test_runpy) rather than
+        # relying on this function (as test_importhooks and test_pkg do
+        # currently).  Implicitly imported *real* modules should be left alone
+        # (see issue 10556).
+        sys.modules.update(oldmodules)
+
 
 try:
     from importlib.machinery import ModuleSpec
@@ -180,6 +204,10 @@ def tearDownClass(cls):
         except AttributeError:
             pass
 
+    def setUp(self):
+        modules = modules_setup()
+        self.addCleanup(modules_cleanup, *modules)
+
 
 class ZipSetup(ZipSetupBase):
     ZIP_MODULE = zipdata01                          # type: ignore