diff --git a/Tests/test_file_spider.py b/Tests/test_file_spider.py
index 3b1953aac..df385208f 100644
--- a/Tests/test_file_spider.py
+++ b/Tests/test_file_spider.py
@@ -15,7 +15,7 @@ TEST_FILE = "Tests/images/hopper.spider"
 
 
 def teardown_module() -> None:
-    del Image.EXTENSION[".spider"]
+    Image.EXTENSION.pop(".spider", None)
 
 
 def test_sanity() -> None:
diff --git a/tox.ini b/tox.ini
index de18946ef..aede5fcdc 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,11 +9,16 @@ env_list =
 [testenv]
 deps =
     numpy
+    pytest-sugar
 extras =
     tests
 commands =
     {envpython} selftest.py
-    {envpython} -m pytest -W always {posargs}
+    {envpython} -m pytest \
+      --dist worksteal \
+      --numprocesses auto \
+      -W always \
+      {posargs}
 
 [testenv:lint]
 skip_install = true