fix test case again and again, what the fffff happend on windows

tests/test_create.py

@@ -103,22 +103,18 @@ def run_command(command, prefix, *arguments):
 
 @contextmanager
 def make_temp_env(*packages, **kwargs):
-    import os
     prefix = kwargs.pop('prefix', None) or make_temp_prefix()
+    assert isdir(prefix), prefix
     prefix = escape_for_winpath(prefix)
     with stderr_log_level(DEBUG, 'conda'), stderr_log_level(DEBUG, 'requests'):
         with disable_logger('fetch'), disable_logger('dotupdate'):
             try:
                 # try to clear any config that's been set by other tests
                 reset_context([join(prefix, 'condarc')])
                 run_command(Commands.CREATE, prefix, *packages)
-                os.environ["CONDA_ROOT"] = prefix
-                os.environ["CONDA_PREFIX"] = prefix
                 yield prefix
             finally:
                 rmtree(prefix, ignore_errors=True)
-                os.environ.pop('CONDA_ROOT', None)
-                os.environ.pop('CONDA_PREFIX', None)
 
 
 def reload_config(prefix):