Handler testing in App Engine fails: webtest import errors

I can't make any sense of this error:

======================================================================
ERROR: test_webtest (unittest2.loader.ModuleImportFailure)
----------------------------------------------------------------------
ImportError: Failed to import test module: test_webtest
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/unittest2/loader.py", line 260, in _find_tests
    module = self._get_module_from_name(name)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/unittest2/loader.py", line 238, in _get_module_from_name
    __import__(name)
  File "/Users/chris/Documents/gae/tasker/test/test_webtest.py", line 4, in <module>
    import webtest
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/webtest/__init__.py", line 9, in <module>
    from webtest.app import TestApp
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/webtest/app.py", line 65, in <module>
    class TestRequest(webob.BaseRequest):
AttributeError: 'module' object has no attribute 'BaseRequest'

The situation is:

I'm trying to set up handler unit tests for my App Engine app.
I'm following this tutorial for a unit test framework, including the bash script at the bottom of the page, verbatim.
I'm running tests from the terminal with this command:

./run_tests.py /usr/local/google_appengine test/
I'm using this tutorial for structuring my handler tests. But it never gets past the imports. All I have to do is this in test/test_webtest.py to generate the error:
```
import webtest
```

I have webtest installed:

$ pip install WebTest
Requirement already satisfied (use --upgrade to upgrade): WebTest in /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages
Requirement already satisfied (use --upgrade to upgrade): six in /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages (from WebTest)
Requirement already satisfied (use --upgrade to upgrade): WebOb>=1.2 in /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages (from WebTest)
Requirement already satisfied (use --upgrade to upgrade): waitress in /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages (from WebTest)
Requirement already satisfied (use --upgrade to upgrade): beautifulsoup4 in /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages (from WebTest)
Requirement already satisfied (use --upgrade to upgrade): distribute in /Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/site-packages/distribute-0.6.28-py2.7.egg (from waitress->WebTest)

I am running all my tests at once, including older ones that pass with no errors. But importing webtest into any of them generates the error at the top. Why?

Solution

This turned out to be a silly problem with my different python environments.

The pip and python in my path were linked to /user/local/bin/python. That's where webtest was, in fact, installed.

The code I had copied from the tutorial, however, had this hashbang: #!/usr/bin/python so when I ran it with ./run_tests.py, it ran in the environment where webtest wasn't installed.

Running either python ./run_tests.py or changing the hashbang to #!/user/local/bin/python fixed the problem.