tests: clone pylint locally for CI. Fixes #250

Pylint 2.4.0 (pylint-dev/pylint@33b8185) removed the 'test' module from
its package and this broke our tests. Clone the sources locally
and adjust the paths so that CI continues to work.

.travis.yml

@@ -26,6 +26,9 @@ matrix:
     - { stage: test, python: 3.6, env: TOXENV=readme }
     - { stage: build_and_package_sanity, python: 3.6, env: SANITY_CHECK=1 }
 
+before_install:
+  - git clone --depth 1 https://github.com/PyCQA/pylint.git
+
 install:
   - pip install tox-travis
   - pip install -e .[for_tests]

pylint_django/tests/test_func.py

@@ -4,8 +4,15 @@
 import pytest
 
 import pylint
-# because there's no __init__ file in pylint/test/
-sys.path.append(os.path.join(os.path.dirname(pylint.__file__), 'test'))
+
+if pylint.__version__ >= '2.4':
+    # after version 2.4 pylint stopped shipping the test directory
+    # as part of the package so we check it out locally for testing
+    sys.path.append(os.getenv('HOME'), 'pylint', 'tests'))
+else:
+    # because there's no __init__ file in pylint/test/
+    sys.path.append(os.path.join(os.path.dirname(pylint.__file__), 'test'))
+
 import test_functional  # noqa: E402
 
 # alter sys.path again because the tests now live as a subdirectory