Problem with AGP Python Toolbox executing Unittest

[BernhardEhrminger]

In Module FileCount.py I have a simple Python Unittest, which tests that the number of files in current directory is greater than zero, so the test should never fail.

import unittest
import pathlib


class Test(unittest.TestCase):

    def setUp(self):
        pass

    def tearDown(self):
        pass

    def test_file_count(self):
        self.assertGreater(
            len(list(pathlib.Path().cwd().glob('*'))), 0)
        pass

The Python Tool-Class referencing the Unittest is like:

class DemoUnittest(object):

    def __init__(self):
        """Define the tool (tool name is the name of the class)."""
        self.label = "Demo_Unittest"
        self.description = "Execute a Unittest"
        self.canRunInBackground = True

    def getParameterInfo(self):
        """Define parameter definitions"""
        params = None
        return params

    def isLicensed(self):
        """Set whether tool is licensed to execute."""
        return True

    def updateParameters(self, parameters):
        """Modify the values and properties of parameters before internal validation is performed.  This method is called whenever a parameter has been changed."""
        return

    def updateMessages(self, parameters):
        """Modify the messages created by internal validation for each tool parameter. This method is called after internal validation."""
        return

    def execute(self, parameters, messages):
        """The source code of the tool."""
        try:
            self.result = unittest.TextTestRunner().run(
                unittest.TestLoader().loadTestsFromModule(
                    module = FileCount))
            arcpy.AddMessage(self.result)
        except Exception as e:
            arcpy.AddMessage(str(e))
        return True

    def postExecute(self, parameters):
        arcpy.AddMessage(self.result)
        """This method takes place after outputs are processed and added to the display."""
        return

When running the Python Tool in ArcGIS Pro I get the following result:

So from the screen dump above, I conclude the Unittest performed as expected (OK).

But why is ArcGIS Pro telling me erroneously  "Failed to execute (DemoUnittest)"?

Thank You for your attention.

[Luke_Pinner]

The default output stream for unittest.TextTestRunner is sys.stderr and I don't know and haven't tested, but  perhaps ArcGIS notices this and assumes there's been an error?

[BernhardEhrminger · Accepted solution]

the class constructor unittest.TextTestRunner has an argument stream, which can be initialized to sys.stdout. In this case the problem with failing tools does not exist.

[BernhardEhrminger]

thank you Luke, the situation is like you pointed out.