Force cpu usage on macos-latest runners (#114)

* Force cpu usage on macos-latest runners

* Moved torch_device setting to root conftest

* Go back to setting keras global state in brainglobe-workflows

* Force backend env variable to be set with a fixture before importing keras

* Add input that should cause an error only on macos-latest

* Run set_device_arm_macos_ci on all darwin platforms

* Try using the CI variable instead

* Pass GITHUB_* env variables via tox

* Moved passenv to the bottom of testenv to match other pyproject files

* Use force_cpu function from cellfinder

* Removed manual setting of GITHUB_ACTIONS

pyproject.toml

@@ -147,4 +147,7 @@ commands =
 description =
     Run tests
     coredev: Run tests with the development version of cellfinder
+passenv =
+    CI
+    GITHUB_*
 """

tests/conftest.py

@@ -0,0 +1,24 @@
+import os
+
+import pytest
+import torch
+from cellfinder.core.tools.system import force_cpu
+
+
+@pytest.fixture(scope="session", autouse=True)
+def set_backend_torch():
+    os.environ["KERAS_BACKEND"] = "torch"
+
+
+@pytest.fixture(scope="session", autouse=True)
+def set_device_arm_macos_ci():
+    """
+    Ensure that the device is set to CPU when running on arm based macOS
+    GitHub runners. This is to avoid the following error:
+    https://discuss.pytorch.org/t/mps-back-end-out-of-memory-on-github-action/189773/5
+    """
+    if (
+        os.getenv("GITHUB_ACTIONS") == "true"
+        and torch.backends.mps.is_available()
+    ):
+        force_cpu()