diff --git a/.gitignore b/.gitignore
index 5863b08..34e27fa 100644
--- a/.gitignore
+++ b/.gitignore
@@ -245,3 +245,6 @@ $RECYCLE.BIN/
 
 # Windows shortcuts
 *.lnk
+
+# Visualization side effects
+**/visualization_results.pdf
diff --git a/tests/test_class_optimize.py b/tests/test_class_optimize.py
index 814a1bc..4655aa3 100644
--- a/tests/test_class_optimize.py
+++ b/tests/test_class_optimize.py
@@ -32,3 +32,7 @@ def test_optimize(fn_in, fn_out):
     # This does not assert that the optimization always gives the same result!
     # Reproducibility and mathematical accuracy should be tested on the level of individual components.
     assert set(ergebnis) == set(expected_output_data)
+
+    # The function creates a visualization result PDF as a side-effect.
+    fp_viz = Path(".") / "visualization_results.pdf"
+    assert fp_viz.exists()
diff --git a/visualization_results.pdf b/visualization_results.pdf
deleted file mode 100644
index 7f4d499..0000000
Binary files a/visualization_results.pdf and /dev/null differ