Arm/Cortex-M backend: Share deterministic test seed handling

backends/arm/test/conftest.py

@@ -26,7 +26,13 @@ def pytest_configure(config):
         pytest._test_options["llama_inputs"] = config.option.llama_inputs  # type: ignore[attr-defined]
 
     logging.basicConfig(stream=sys.stdout)
-    _set_random_seed()
+    seed, seed_label = _setup_random_seed()
+    config._test_seed = seed
+    config._test_seed_label = seed_label
+
+
+def pytest_report_header(config):
+    return config._test_seed_label
 
 
 def pytest_collection_modifyitems(config, items):
@@ -64,42 +70,45 @@ def pytest_sessionfinish(session, exitstatus):
 
 
 @pytest.fixture(autouse=True)
-def set_random_seed():
+def set_random_seed(request):
     """Control random numbers in Arm test suite. Default behavior is to use a
     fixed seed (0), which ensures reproducible tests. Use the env variable
-    ARM_TEST_SEED to set a custom seed, or set it to RANDOM for random seed
+    TEST_SEED to set a custom seed, or set it to RANDOM for random seed
     behavior.
 
     Examples:
     As default use fixed seed (0) for reproducible tests
         pytest --config-file=/dev/null --verbose -s --color=yes  backends/arm/test/ops/test_avg_pool.py -k <TESTCASE>
     Use a random seed for each test
-        ARM_TEST_SEED=RANDOM pytest --config-file=/dev/null --verbose -s --color=yes  backends/arm/test/ops/test_avg_pool.py -k <TESTCASE>
+        TEST_SEED=RANDOM pytest --config-file=/dev/null --verbose -s --color=yes  backends/arm/test/ops/test_avg_pool.py -k <TESTCASE>
     Rerun with a specific seed
-        ARM_TEST_SEED=3478246 pytest --config-file=/dev/null --verbose -s --color=yes  backends/arm/test/ops/test_avg_pool.py -k <TESTCASE>
+        TEST_SEED=3478246 pytest --config-file=/dev/null --verbose -s --color=yes  backends/arm/test/ops/test_avg_pool.py -k <TESTCASE>
 
     """
-    _set_random_seed()
+    _set_random_seed(request.config._test_seed)
 
 
-def _set_random_seed():
-    import torch
-
-    seed_env = os.environ.get("ARM_TEST_SEED", "0")
+def _setup_random_seed():
+    seed_env = os.environ.get("TEST_SEED", "0")
     if seed_env == "RANDOM":
         random.seed()  # reset seed, in case any other test has fiddled with it
         seed = random.randint(0, 2**32 - 1)  # nosec B311 - non-crypto seed for tests
-        torch.manual_seed(seed)
-        print(f" ARM_TEST_SEED=RANDOM using:{seed} ", end=" ")
+        seed_label = f"TEST_SEED=RANDOM using:{seed}"
     elif str.isdigit(seed_env):
         seed = int(seed_env)
-        random.seed(seed)
-        torch.manual_seed(seed)
-        print(f" ARM_TEST_SEED={seed} ", end=" ")
+        seed_label = f"TEST_SEED={seed}"
     else:
-        raise TypeError(
-            "ARM_TEST_SEED env variable must be integers or the string RANDOM"
-        )
+        raise TypeError("TEST_SEED env variable must be integers or the string RANDOM")
+
+    _set_random_seed(seed)
+    return seed, seed_label
+
+
+def _set_random_seed(seed):
+    import torch
+
+    random.seed(seed)
+    torch.manual_seed(seed)
 
 
 # ==== End of Pytest fixtures =====

backends/cortex_m/test/conftest.py

@@ -1,12 +1,17 @@
 # Copyright (c) Meta Platforms, Inc. and affiliates.
 # All rights reserved.
+# Copyright 2026 Arm Limited and/or its affiliates.
 #
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
+import os
+import random
+
 import pytest
 from executorch.backends.cortex_m.target_config import CortexMTargetConfig
 
+
 _DEFAULT_TARGET = "cortex-m55"
 
 
@@ -29,7 +34,7 @@ def _selected_targets(config) -> list[str]:
 
 
 def pytest_report_header(config):
-    return f"cortex-m op-test targets: {', '.join(_selected_targets(config))}"
+    return f"cortex-m op-test targets: {', '.join(_selected_targets(config))} {config._test_seed_label}"
 
 
 def pytest_generate_tests(metafunc):
@@ -46,3 +51,43 @@ def cortex_m_target(request) -> CortexMTargetConfig:
     the AoT target config (and, for implementation tests, the matching prebuilt
     FVP runner)."""
     return CortexMTargetConfig.from_target_string(request.param)
+
+
+def pytest_configure(config):
+    seed, seed_label = _setup_random_seed()
+    config._test_seed = seed
+    config._test_seed_label = seed_label
+
+
+@pytest.fixture(autouse=True)
+def set_random_seed(request):
+    """Control random numbers in the Cortex-M test suite.
+
+    By default this uses a fixed seed (0) for reproducible tests. Use
+    TEST_SEED to set a custom seed, or set it to RANDOM for random seed
+    behavior.
+    """
+    _set_random_seed(request.config._test_seed)
+
+
+def _setup_random_seed():
+    seed_env = os.environ.get("TEST_SEED", "0")
+    if seed_env == "RANDOM":
+        random.seed()  # reset seed, in case any other test has fiddled with it
+        seed = random.randint(0, 2**32 - 1)  # nosec B311 - non-crypto seed for tests
+        seed_label = f"TEST_SEED=RANDOM using:{seed}"
+    elif str.isdigit(seed_env):
+        seed = int(seed_env)
+        seed_label = f"TEST_SEED={seed}"
+    else:
+        raise TypeError("TEST_SEED env variable must be integers or the string RANDOM")
+
+    _set_random_seed(seed)
+    return seed, seed_label
+
+
+def _set_random_seed(seed):
+    import torch
+
+    random.seed(seed)
+    torch.manual_seed(seed)