Switch to matplotlib agg backend for tests (#101)

Should fix somewhat randomly occurring matplotlib/tk failures

Author: dweindl

tests/test_visualization.py

@@ -1,15 +1,19 @@
 import subprocess
 import warnings
 from os import path
-from tempfile import TemporaryDirectory
 from pathlib import Path
+from tempfile import TemporaryDirectory
+
 import matplotlib.pyplot as plt
 import pytest
 from petab.C import *
 from petab.visualize import (plot_data_and_simulation,
                              plot_measurements_by_observable,
                              save_vis_spec)
 
+# Avoid errors when plotting without X server
+plt.switch_backend('agg')
+
 
 @pytest.fixture
 def data_file_Fujita():

tests/test_visualization_new_structure.py

@@ -1,10 +1,15 @@
 from os import path
 from tempfile import TemporaryDirectory
+
+import matplotlib.pyplot as plt
 import pytest
 from petab.C import *
 from petab.visualize import plot_with_vis_spec, plot_without_vis_spec
 from petab.visualize.plotting import VisSpecParser
 
+# Avoid errors when plotting without X server
+plt.switch_backend('agg')
+
 
 @pytest.fixture
 def data_file_Fujita():