Switched our backend to be a normal fixture in tests (#3665)

diff --git a/tests/conftest.py b/tests/conftest.py
index 66a3cd6..c21f4dc 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -8,30 +8,28 @@
 
 from cryptography.hazmat.backends.openssl import backend as openssl_backend
 
-from .utils import check_backend_support, skip_if_empty
+from .utils import check_backend_support
 
 
 def pytest_report_header(config):
     return "OpenSSL: {0}".format(openssl_backend.openssl_version_text())
 
 
-def pytest_generate_tests(metafunc):
-    if "backend" in metafunc.fixturenames:
-        filtered_backends = []
-        required_interfaces = [
-            mark.kwargs["interface"]
-            for mark in metafunc.function.requires_backend_interface
-        ]
-        if all(
-            isinstance(openssl_backend, iface) for iface in required_interfaces
-        ):
-            filtered_backends.append(openssl_backend)
-
-        # If you pass an empty list to parametrize Bad Things(tm) happen
-        # as of pytest 2.6.4 when the test also has a parametrize decorator
-        skip_if_empty(filtered_backends, required_interfaces)
-
-        metafunc.parametrize("backend", filtered_backends)
+@pytest.fixture()
+def backend(request):
+    required_interfaces = [
+        mark.kwargs["interface"]
+        for mark in request.node.get_marker("requires_backend_interface")
+    ]
+    if all(
+        isinstance(openssl_backend, iface) for iface in required_interfaces
+    ):
+        return openssl_backend
+    pytest.skip(
+        "OpenSSL doesn't implement required interfaces: {0}".format(
+            required_interfaces
+        )
+    )
 
 
 @pytest.mark.trylast