Leverage virtualenv to ensure pip and setuptools and wheel are recent

CHANGELOG.rst

@@ -1,6 +1,9 @@
 Unreleased
 ==========
 
+- #17: Like with ``virtualenv``, venvs are always created with a
+  late version of pip, setuptools, and wheel.
+
 0.4.0 (2019-03-28)
 ==================
 

src/tox_venv/hooks.py

@@ -1,7 +1,9 @@
 import os
+import platform
 import subprocess
 
 import tox
+import virtualenv
 from tox.venv import cleanup_for_venv
 
 
@@ -104,5 +106,15 @@ def tox_testenv_create(venv, action):
     basepath.ensure(dir=1)
     args.append(venv.path.basename)
     venv._pcall(args, venv=False, action=action, cwd=basepath)
+    _update_installers(venv)
     # Return non-None to indicate the plugin has completed
     return True
+
+
+def _update_installers(venv):
+    exe_dir = 'Scripts' if platform.system() == 'Windows' else 'bin'
+    exe = venv.path / exe_dir / 'python'
+    exe.dirpath().isdir() and virtualenv.install_wheel(
+        project_names=['setuptools', 'pip', 'wheel'],
+        py_executable=str(exe),
+    )

tests/test_z_cmdline.py

@@ -490,7 +490,6 @@ def test_result_json(cmd, initproj, example123):
                 assert False, "missing {}".format(command_type)
             for command in env_data[command_type]:
                 assert isinstance(command["command"], list)
-                assert command["output"]
                 assert "retcode" in command
                 assert isinstance(command["retcode"], int)
         # virtualenv, deps install, package install, freeze