examples_test.py cannot be run in parallel

[elcorto]

The order of test execution is given by the order of tests in a test script. In examples_test.py, test_basic_ex01 is run first, creating be_model.zip, which is needed by some other tests in the script.

When test are executed in parallel (e.g. using pytest-xdist), the order is random and some tests that depend on the existence of that artifact will fail.

[elcorto]

A simple fix that doesn't depend on pytest plugins is:

diff --git a/test/examples_test.py b/test/examples_test.py
index 8fb82eac..531f0018 100644
--- a/test/examples_test.py
+++ b/test/examples_test.py
@@ -1,16 +1,28 @@
 """Test whether the examples are still working."""

 import runpy
+import os

 import pytest


+# There is https://github.com/RKrahl/pytest-dependency and
+# https://github.com/pytest-dev/pytest-order but we like to keep in simple
+# here. When running in parallel (pytest-xdist), we execute ex01 at most twice,
+# which is OK.
+def check_and_create_ex01_artifact():
+    if not os.path.exists("be_model.zip"):
+        print("Running example basic/ex01 in preparation another example")
+        runpy.run_path("../examples/basic/ex01_train_network.py")
+
+
 @pytest.mark.examples
 class TestExamples:
     def test_basic_ex01(self):
         runpy.run_path("../examples/basic/ex01_train_network.py")

     def test_basic_ex02(self):
+        check_and_create_ex01_artifact()
         runpy.run_path("../examples/basic/ex02_test_network.py")

     def test_basic_ex03(self):
@@ -20,9 +32,11 @@ class TestExamples:
         runpy.run_path("../examples/basic/ex04_hyperparameter_optimization.py")

     def test_basic_ex05(self):
+        check_and_create_ex01_artifact()
         runpy.run_path("../examples/basic/ex05_run_predictions.py")

     def test_basic_ex06(self):
+        check_and_create_ex01_artifact()
         runpy.run_path("../examples/basic/ex06_ase_calculator.py")