add TestNormalizeBackend

test/test_backends.py

@@ -2,30 +2,58 @@
 
 import pytest
 
-from urllib3.backends import Backend as UserSpecifiedBackend
-from urllib3._backends._loader import load_backend
+import urllib3
+from urllib3.backends import Backend
+from urllib3._backends._loader import normalize_backend, load_backend
 
 
-class TestLoadBackend(object):
+requires_async_pool_manager = pytest.mark.skipif(
+    not hasattr(urllib3, "AsyncPoolManager"),
+    reason="async backends require AsyncPoolManager",
+)
+
+
+requires_sync_pool_manager = pytest.mark.skipif(
+    hasattr(urllib3, "AsyncPoolManager"),
+    reason="sync backends cannot be used with AsyncPoolManager",
+)
+
+
+class TestNormalizeBackend(object):
     """
-    We assert that we are able to import compatible backends,
-    and that we fail correctly if we attempt to use an unavailable or unknown backend.
+    Assert that we fail correctly if we attempt to use an unknown or incompatible backend.
     """
-    def test_dummy(self):
-        with pytest.raises(ImportError):
-            load_backend("dummy")
+    def test_unknown(self):
+        with pytest.raises(ValueError):
+            normalize_backend("_unknown")
 
+    @requires_sync_pool_manager
     def test_sync(self):
-        load_backend("sync")
-        load_backend(UserSpecifiedBackend("sync"))
+        assert normalize_backend(Backend("sync")) == Backend("sync")
+        assert normalize_backend("sync") == Backend("sync")
+        assert normalize_backend(None) == Backend("sync")
 
-    @pytest.mark.skipif(
-        sys.version_info < (3, 5),
-        reason="async backends require Python 3.5 or greater",
-    )
+    @requires_async_pool_manager
     def test_async(self):
-        load_backend("trio")
-        load_backend("twisted")
+        assert normalize_backend(Backend("trio")) == Backend("trio")
+        assert normalize_backend("twisted") == Backend("twisted")
+
+        with pytest.raises(ValueError):
+            normalize_backend(Backend("sync"))
+
+        from twisted.internet import reactor
+        assert normalize_backend(Backend("twisted", reactor=reactor)) == Backend("twisted", reactor=reactor)
 
+
+class TestLoadBackend(object):
+    """
+    Assert that we can load a normalized backend
+    """
+    @requires_sync_pool_manager()
+    def test_sync(self):
+        load_backend(normalize_backend("sync"))
+
+    @requires_async_pool_manager()
+    def test_async(self):
         from twisted.internet import reactor
-        load_backend(UserSpecifiedBackend("twisted", reactor=reactor))
+        load_backend(Backend("twisted", reactor=reactor))