tests: make test_plot_allfreqs_single_run a standalone test
diff --git a/tests/test_plot_utils.py b/tests/test_plot_utils.py
index 2f51cb2..2a5f178 100644
--- a/tests/test_plot_utils.py
+++ b/tests/test_plot_utils.py
@@ -135,5 +135,9 @@
         plot_utils.plot_allfreqs(runs, self.map_label, width=20)
         matplotlib.pyplot.close('all')
 
-        plot_utils.plot_allfreqs([run1], self.map_label, width=20)
+    def test_plot_allfreqs_single_run(self):
+        """plot_utils.plot_allfreqs() can be used with a single run"""
+        run = cr2.Run()
+
+        plot_utils.plot_allfreqs([run], self.map_label)
         matplotlib.pyplot.close('all')