catkin_add_nosetests runs with inconsistent pythonpath (depending whether it's a clean build or a rebuild)

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I seem to have extremely similar (almost identical) symptoms to an old closed question that got closed with no feedback ( https://answers.ros.org/question/2627... ). Hopefully this thread doesn't suffer the same fate!

It's a relatively simple python package with some nosetests. The tests fail sometimes and pass sometimes. It seems to be directly correlated with clean build vs rebuild. Clean always fails, non-clean rebuild always passes.

I think it may be a bug in ROS/catkin where the python path is getting set inconsistently on build/rebuild. Here's what I've documented so far:

Scenario A: clean build. Tests fail.

• run rm -r build devel
• run catkin_make
• run source devel/setup.bash
• run catkin_make run_tests or catkin_make run_tests_<package-name>
• Result: errors on including python files from the module this package wraps, e.g. ImportError: No module named <module>
• Without altering any files that would cause a re-build, re-running the same run_tests command produces the same results
• (similar errors for any attempts to include from nested sub-modules)

Scenario B: a dirty re-build, no changes to the files besides last-modified date. Tests pass.

• Setup: Do Scenario A, or just don't wipe build & devel after doing whatever else.
• touch the CMakeLists.txt file in the project in question
• run catkin_make run_tests_<package-name>
• Result: The 'broken' tests files now load & pass successfully.

Additionally, the tests pass if I run them manually by calling nosetests on the command line. My actual PYTHONPATH after sourcing setup.bash is what I would expect (/home/evan/<repo-name>/devel/lib/python2.7/dist-packages:/opt/ros/kinetic/lib/python2.7/dist-packages)

I did a little work to verify python path during test execution and here's the steps+results:

• Added the following to the top of my test file: sys.stderr.write('PYTHONPATH=' + os.environ['PYTHONPATH'] + '\n')
• Re-ran Scenario A
  • The debug/stderr output was PYTHONPATH=/opt/ros/kinetic/lib/python2.7/dist-packages
• Re-ran Scenario B
  • The debug/stderr output was PYTHONPATH=/home/evan/<repo-name>/devel/lib/python2.7/dist-packages:/opt/ros/kinetic/lib/python2.7/dist-packages

PYTHONPATH seems like something that should be the same after building & running setup.bash no matter how (nor how many times) I build/run it, not something that changes on a re-build. Is this in fact a ROS/catkin bug of some kind as it seems from the above, or have I somehow misconfigured something?

my setup.py is straightforward/simple:

from distutils.core import setup
from catkin_pkg.python_setup import generate_distutils_setup

# fetch values from package.xml
setup_args = generate_distutils_setup(
    packages=['packagename'],
    scripts=['scripts'],
    package_dir={'': 'scripts'}
)

setup(**setup_args)

My directory structure is

packagename/
  scripts/
    packagename/
      class1.py
      class2.py
      etc.py
      submodule/
        class3.py
  tests/
    class1_test.py
    class2_test.py
    etc_test.py
  CMakeLists.txt
  package.xml
  setup.py

sample test file structure:

import unittest
from mock import Mock
from mock import MagicMock

import os
from packagename.class1 import blah
from packagename.submodule.class3 import blah3

package.xml:

<?xml version="1.0"?>
<package>
  <name>packagename</name>
  <version>0.0.0</version ...