diff --git a/run_tests.py b/run_tests.py
index b3bcee20f..6e9c6ce9d 100755
--- a/run_tests.py
+++ b/run_tests.py
@@ -26,6 +26,7 @@ from io import StringIO
 from enum import Enum
 from glob import glob
 from pathlib import Path
+from unittest import mock
 from mesonbuild import compilers
 from mesonbuild import dependencies
 from mesonbuild import mesonlib
@@ -255,16 +256,11 @@ def ensure_backend_detects_changes(backend):
         time.sleep(1)
 
 def run_mtest_inprocess(commandlist):
-    old_stdout = sys.stdout
-    sys.stdout = mystdout = StringIO()
-    old_stderr = sys.stderr
-    sys.stderr = mystderr = StringIO()
-    try:
+    stderr = StringIO()
+    stdout = StringIO()
+    with mock.patch.object(sys, 'stdout', stdout), mock.patch.object(sys, 'stderr', stderr):
         returncode = mtest.run_with_args(commandlist)
-    finally:
-        sys.stdout = old_stdout
-        sys.stderr = old_stderr
-    return returncode, mystdout.getvalue(), mystderr.getvalue()
+    return returncode, stdout.getvalue(), stderr.getvalue()
 
 def clear_meson_configure_class_caches():
     compilers.CCompiler.library_dirs_cache = {}
@@ -275,22 +271,14 @@ def clear_meson_configure_class_caches():
     dependencies.PkgConfigDependency.class_pkgbin = mesonlib.PerMachine(None, None)
 
 def run_configure_inprocess(commandlist, env=None):
-    old_stdout = sys.stdout
-    sys.stdout = mystdout = StringIO()
-    old_stderr = sys.stderr
-    sys.stderr = mystderr = StringIO()
-    old_environ = os.environ.copy()
-    if env is not None:
-        os.environ.update(env)
-    try:
-        returncode = mesonmain.run(commandlist, get_meson_script())
-    finally:
-        sys.stdout = old_stdout
-        sys.stderr = old_stderr
-        clear_meson_configure_class_caches()
-        os.environ.clear()
-        os.environ.update(old_environ)
-    return returncode, mystdout.getvalue(), mystderr.getvalue()
+    stderr = StringIO()
+    stdout = StringIO()
+    with mock.patch.dict(os.environ, env or {}), mock.patch.object(sys, 'stdout', stdout), mock.patch.object(sys, 'stderr', stderr):
+        try:
+            returncode = mesonmain.run(commandlist, get_meson_script())
+        finally:
+            clear_meson_configure_class_caches()
+    return returncode, stdout.getvalue(), stderr.getvalue()
 
 def run_configure_external(full_command, env=None):
     pc, o, e = mesonlib.Popen_safe(full_command, env=env)
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: