diff --git a/conftest.py b/conftest.py
new file mode 100644
index 0000000..3924c56
--- /dev/null
+++ b/conftest.py
@@ -0,0 +1,5 @@
+import matplotlib as mpl
+
+# chose the matplotlib backend that can only generate pngs
+# but not interact with the os (better for testing)
+mpl.use("Agg")