Use pytest-isolate to make tests more reliable

pyproject.toml

@@ -5,4 +5,4 @@ markers = [
 ]
 asyncio_mode = "auto"
 # Default timeout of 5 minutes
-timeout = 300
+isolate_timeout = 300

python/tests/requirements.txt

@@ -1,5 +1,5 @@
 pytest
-pytest-timeout
 pytest-asyncio
+pytest-isolate
 pytest-xdist
 pyright

scripts/common-setup.sh

@@ -172,15 +172,16 @@ run_test_groups() {
     pkill -9 pytest || true
     sleep 2
     # Conditionally set environment variable for pytest
+    # Isolate runs each test in a separate forked process which enhances reliability.
     if [[ "$enable_v1" == "1" ]]; then
       MONARCH_HOST_MESH_V1_REMOVE_ME_BEFORE_RELEASE=1 \
-      LC_ALL=C pytest python/tests/ -s -v -m "not oss_skip" \
+      LC_ALL=C pytest --isolate -n auto python/tests/ -s -v -m "not oss_skip" \
         --ignore-glob="**/meta/**" \
         --dist=no \
         --group=$GROUP \
         --splits=10
     else
-      LC_ALL=C pytest python/tests/ -s -v -m "not oss_skip" \
+      LC_ALL=C pytest --isolate -n auto python/tests/ -s -v -m "not oss_skip" \
         --ignore-glob="**/meta/**" \
         --dist=no \
         --group=$GROUP \