Use batch (something weird going on with that powershell) and make the virtualenv pin a minimum requirement.

Author: ionelmc

appveyor.yml

@@ -15,20 +15,16 @@ init:
   - ps: echo $env:TOXENV
   - ps: ls C:\Python*
 install:
-  - ps: |
-      if ($env:TOXENV -notmatch 'pypy') {
+  - |
+    IF "%TOXENV:~0,4%" == "pypy" (
         choco install --no-progress python.pypy
-        $env:PATH = "C:\tools\pypy\pypy;$env:PATH"
-        pypy --version
-      }
-
-  # Upgrade virtualenv for e.g. more-itertools to be handled properly.
-  # Pin it to work around https://github.com/tox-dev/tox/issues/1389.
-  - C:\Python35\python -m pip install -U virtualenv==16.5.0
-  - C:\Python35\python -m pip install tox
+        C:\tools\pypy\pypy --version
+    )
+  - C:\Python37\python -m pip install -U "virtualenv>=16.5.0"
+  - C:\Python37\python -m pip install tox
 
 test_script:
-  - C:\Python35\python -m tox
+  - C:\Python37\python -m tox
 
 on_failure:
   - ps: dir "env:"

ci/templates/appveyor.yml

@@ -14,18 +14,16 @@ init:
   - ps: echo $env:TOXENV
   - ps: ls C:\Python*
 install:
-  # install pypy using choco (redirect to a file and write to console in case
-  # choco install returns non-zero, because choco install python.pypy is too
-  # noisy)
-  - choco install python.pypy > pypy-inst.log 2>&1 || (type pypy-inst.log & exit /b 1)
-  - set PATH=C:\tools\pypy\pypy;%PATH% # so tox can find pypy
-  - echo PyPy installed
-  - pypy --version
-
-  - C:\Python35\python -m pip install tox
+  - |
+    IF "%TOXENV:~0,4%" == "pypy" (
+        choco install --no-progress python.pypy
+        C:\tools\pypy\pypy --version
+    )
+  - C:\Python37\python -m pip install -U "virtualenv>=16.5.0"
+  - C:\Python37\python -m pip install tox
 
 test_script:
-  - C:\Python35\python -m tox
+  - C:\Python37\python -m tox
 
 on_failure:
   - ps: dir "env:"