Use cross platform Path compatibility module in test.

tests/integration/test_install_twists.py

@@ -359,15 +359,15 @@ def test_multiple_editable_packages_should_not_race(PipenvInstance, pypi, tmpdir
 """
     # Unzip tarballs to known location, and update Pipfile template.
     for pkg_name, file_name in pkgs.items():
-        source_path = os.path.abspath(os.path.join(testsroot, "pypi", file_name))
-        unzip_path = tmpdir.join(pkg_name)
+        source_path = Path(testsroot, "pypi", file_name)
+        unzip_path = Path(tmpdir.strpath, pkg_name)
 
         import tarfile
 
         with tarfile.open(source_path, "r:gz") as tgz:
             tgz.extractall(path=tmpdir.strpath)
 
-        pipfile_string += '"{0}" = {{path = "{1}", editable = true}}\n'.format(pkg_name, unzip_path.strpath)
+        pipfile_string += '"{0}" = {{path = "{1}", editable = true}}\n'.format(pkg_name, unzip_path)
 
     with PipenvInstance(pypi=pypi, chdir=True) as p:
         print(pipfile_string)