Set environment before calling which

Signed-off-by: Dan Ryan <dan@danryan.co>

.vsts-ci/phases/run-tests.yml

@@ -14,7 +14,7 @@ steps:
    export GIT_SSL_CAINFO="$(python -m certifi)"
    export LANG="C.UTF-8"
    export PIP_PROCESS_DEPENDENCY_LINKS="1"
-   echo "Path: $PATH"
+   echo "Path $PATH"
    echo "Installing Pipenv…"
    pip install -e "$(pwd)" --upgrade
    pipenv install --deploy --dev

.vsts-ci/steps/run-tests.yml

@@ -8,7 +8,9 @@ steps:
     # https://bugs.python.org/issue18199
     subst T: "$env:TEMP"
     Write-Host "##vso[task.setvariable variable=TEMP]T:\"
+    $env:TEMP='T:\'
     Write-Host "##vso[task.setvariable variable=TMP]T:\"
+    $env:TEMP='T:\'
     Get-ChildItem Env:
     D:\.venv\Scripts\pipenv run pytest -n 4 -ra --ignore=pipenv\patched --ignore=pipenv\vendor --junitxml=test-results.xml tests
   displayName: Run integration tests

pipenv/core.py

@@ -1520,6 +1520,10 @@ def which_pip(allow_global=False):
 def system_which(command, mult=False):
     """Emulates the system's which. Returns None if not found."""
     _which = "which -a" if not os.name == "nt" else "where"
+    os.environ = {
+        vistir.compat.fs_str(k): vistir.compat.fs_str(val)
+        for k, val in os.environ.items()
+    }
     c = delegator.run("{0} {1}".format(_which, command))
     try:
         # Which Not found…
@@ -2223,7 +2227,6 @@ def _launch_windows_subprocess(script):
 
 
 def do_run_nt(script):
-    os.environ = {k: vistir.compat.fs_str(val) for k, val in os.environ.items()}
     p = _launch_windows_subprocess(script)
     p.communicate()
     sys.exit(p.returncode)