added comment

tests.py

@@ -3,7 +3,7 @@
 import tempfile
 
 
-def _exec_notebook(path):
+def exec_notebook(path):
     with tempfile.NamedTemporaryFile(suffix=".ipynb") as fout:
         print(fout.name)
         args = ["jupyter", "nbconvert", "--to", "notebook", "--execute",
@@ -13,14 +13,15 @@ def _exec_notebook(path):
 
 
 def test():
-    _exec_notebook('./example1/0-Workflow.ipynb')
-    _exec_notebook('./example1/1-CreateDataset.ipynb')
-    _exec_notebook('./example1/2-CalculateFeatures.ipynb')
-    _exec_notebook('./example1/3-FitModel.ipynb')
-    _exec_notebook('./example1/4-Predict.ipynb')
-    _exec_notebook('./example2/0-Workflow.ipynb')
-    _exec_notebook('./example2/1-SimulateTree.ipynb')
-    _exec_notebook('./example2/2-SimulateSequences.ipynb')
+# these notebook must be run in order
+    exec_notebook('./example1/0-Workflow.ipynb')
+    exec_notebook('./example1/1-CreateDataset.ipynb')
+    exec_notebook('./example1/2-CalculateFeatures.ipynb')
+    exec_notebook('./example1/3-FitModel.ipynb')
+    exec_notebook('./example1/4-Predict.ipynb')
+    exec_notebook('./example2/0-Workflow.ipynb')
+    exec_notebook('./example2/1-SimulateTree.ipynb')
+    exec_notebook('./example2/2-SimulateSequences.ipynb')
 
 
 if __name__ == '__main__':