Merge pull request #4914 from hroncok/issue4913

Fix pytest tests invocation with custom PYTHONPATH

Author: blueyed

changelog/4913.trivial.rst

@@ -0,0 +1 @@
+Fix pytest tests invocation with custom ``PYTHONPATH``.

testing/test_collection.py

@@ -2,6 +2,7 @@
 from __future__ import division
 from __future__ import print_function
 
+import os
 import pprint
 import sys
 import textwrap
@@ -1108,7 +1109,7 @@ def test_collect_pyargs_with_testpaths(testdir, monkeypatch):
     """
         )
     )
-    monkeypatch.setenv("PYTHONPATH", str(testdir.tmpdir))
+    monkeypatch.setenv("PYTHONPATH", str(testdir.tmpdir), prepend=os.pathsep)
     with root.as_cwd():
         result = testdir.runpytest_subprocess()
     result.stdout.fnmatch_lines(["*1 passed in*"])