Tweak subprocess_run_helper.

On general grounds, an API like
`subprocess_run_helper(func, *args, timeout, **extra_env)`
is problematic because it prevents one from passing an environment
variable called "timeout".

Instead, pass the extra environment variables as a dict, without
unpacking.

(Technically this has been released in 3.5.2 as public API, but 1) I'm
not really sure it should have been a public API to start with (should
we deprecate it and make it private?), and 2) hopefully tweaking that in
3.5.3 with no deprecation is not going to disrupt anyone...  I can still
put in a changelog entry if that's preferred.)

Author: anntzer

lib/matplotlib/testing/__init__.py

@@ -50,39 +50,28 @@ def setup():
     set_reproducibility_for_testing()
 
 
-def subprocess_run_helper(func, *args, timeout, **extra_env):
+def subprocess_run_helper(func, *args, timeout, extra_env=None):
     """
-    Run a function in a sub-process
+    Run a function in a sub-process.
 
     Parameters
     ----------
     func : function
         The function to be run.  It must be in a module that is importable.
-
     *args : str
         Any additional command line arguments to be passed in
-        the first argument to subprocess.run
-
-    **extra_env : Dict[str, str]
-        Any additional environment variables to be set for
-        the subprocess.
-
+        the first argument to ``subprocess.run``.
+    extra_env : dict[str, str]
+        Any additional environment variables to be set for the subprocess.
     """
     target = func.__name__
     module = func.__module__
     proc = subprocess.run(
         [sys.executable,
          "-c",
-         f"""
-from {module} import {target}
-{target}()
-""",
+         f"from {module} import {target}; {target}()",
          *args],
-        env={
-            **os.environ,
-            "SOURCE_DATE_EPOCH": "0",
-            **extra_env
-        },
+        env={**os.environ, "SOURCE_DATE_EPOCH": "0", **(extra_env or {})},
         timeout=timeout, check=True,
         stdout=subprocess.PIPE,
         stderr=subprocess.PIPE,

lib/matplotlib/tests/test_backend_tk.py

@@ -48,10 +48,8 @@ def test_func():
         pytest.importorskip('tkinter')
         try:
             proc = subprocess_run_helper(
-                func, timeout=_test_timeout,
-                MPLBACKEND="TkAgg",
-                MPL_TEST_ESCAPE_HATCH="1"
-            )
+                func, timeout=_test_timeout, extra_env=dict(
+                    MPLBACKEND="TkAgg", MPL_TEST_ESCAPE_HATCH="1"))
         except subprocess.TimeoutExpired:
             pytest.fail("Subprocess timed out")
         except subprocess.CalledProcessError as e:

lib/matplotlib/tests/test_backends_interactive.py

@@ -175,7 +175,7 @@ def test_interactive_backend(env, toolbar):
     proc = _run_helper(_test_interactive_impl,
                        json.dumps({"toolbar": toolbar}),
                        timeout=_test_timeout,
-                       **env)
+                       extra_env=env)
 
     assert proc.stdout.count("CloseEvent") == 1
 
@@ -247,8 +247,7 @@ def _test_thread_impl():
 @pytest.mark.parametrize("env", _thread_safe_backends)
 @pytest.mark.flaky(reruns=3)
 def test_interactive_thread_safety(env):
-    proc = _run_helper(_test_thread_impl,
-                       timeout=_test_timeout, **env)
+    proc = _run_helper(_test_thread_impl, timeout=_test_timeout, extra_env=env)
     assert proc.stdout.count("CloseEvent") == 1
 
 
@@ -447,7 +446,7 @@ def test_lazy_linux_headless(env):
         _lazy_headless,
         env.pop('MPLBACKEND'), env.pop("BACKEND_DEPS"),
         timeout=_test_timeout,
-        **{**env, 'DISPLAY': '', 'WAYLAND_DISPLAY': ''}
+        extra_env={**env, 'DISPLAY': '', 'WAYLAND_DISPLAY': ''}
     )
 
 
@@ -526,10 +525,8 @@ def _test_number_of_draws_script():
 # subprocesses can struggle to get the display, so rerun a few times
 @pytest.mark.flaky(reruns=4)
 def test_blitting_events(env):
-    proc = _run_helper(_test_number_of_draws_script,
-                       timeout=_test_timeout,
-                       **env)
-
+    proc = _run_helper(
+        _test_number_of_draws_script, timeout=_test_timeout, extra_env=env)
     # Count the number of draw_events we got. We could count some initial
     # canvas draws (which vary in number by backend), but the critical
     # check here is that it isn't 10 draws, which would be called if
@@ -585,8 +582,8 @@ def test_figure_leak_20490(env, time_mem):
         acceptable_memory_leakage += 11_000_000
 
     result = _run_helper(
-        _test_figure_leak, str(pause_time), timeout=_test_timeout, **env
-    )
+        _test_figure_leak, str(pause_time),
+        timeout=_test_timeout, extra_env=env)
 
     growth = int(result.stdout)
     assert growth <= acceptable_memory_leakage