tests: Make monkey patching smarter

There are two problems here. The first is that we're doing manual monkey
patching which is fragile and verbose, when unittest.mock is designed
specifically to solve this exact problem. The second is that we're
monkey patching os.environ at two different levels with the same
information. So let's only do it once.

1 files changed, 2 insertions, 15 deletions

diff --git a/run_unittests.py b/run_unittests.py
index 0bcf617ea..da0bf50ce 100755
--- a/run_unittests.py
+++ b/run_unittests.py
@@ -1657,13 +1657,7 @@ class BasePlatformTests(unittest.TestCase):
         self.privatedir = os.path.join(self.builddir, 'meson-private')
         if inprocess:
             try:
-                if override_envvars is not None:
-                    old_envvars = os.environ.copy()
-                    os.environ.update(override_envvars)
-                (returncode, out, err) = run_configure_inprocess(self.meson_args + args + extra_args)
-                if override_envvars is not None:
-                    os.environ.clear()
-                    os.environ.update(old_envvars)
+                (returncode, out, err) = run_configure_inprocess(self.meson_args + args + extra_args, override_envvars)
                 if 'MESON_SKIP_TEST' in out:
                     raise unittest.SkipTest('Project requested skipping.')
                 if returncode != 0:
@@ -1707,15 +1701,8 @@ class BasePlatformTests(unittest.TestCase):
         if not inprocess:
             self._run(self.test_command, workdir=self.builddir, override_envvars=override_envvars)
         else:
-            if override_envvars is not None:
-                old_envvars = os.environ.copy()
-                os.environ.update(override_envvars)
-            try:
+            with mock.patch.dict(os.environ, override_envvars):
                 run_mtest_inprocess(['-C', self.builddir])
-            finally:
-                if override_envvars is not None:
-                    os.environ.clear()
-                    os.environ.update(old_envvars)
 
     def install(self, *, use_destdir=True, override_envvars=None):
         if self.backend is not Backend.ninja: