Enable flake-finder and distributed execution (pytorch#273)

Summary:
Pull Request resolved: pytorch#273

As titled

Reviewed By: huydhn

Differential Revision: D49173802

fbshipit-source-id: 7b1314e184357ec1585aef5ca5bf54e41b947186

Author: guangy10

.github/workflows/_unittest.yml

@@ -37,4 +37,4 @@ jobs:
         # Just need to install executorch, everything else has been setup
         pip install .
         # Run pytest with coverage
-        pytest --cov=./ --cov-report=xml
+        pytest -n auto --cov=./ --cov-report=xml

pyproject.toml

@@ -13,6 +13,7 @@ dependencies=[
   "packaging",
   "parameterized",
   "pytest",
+  "pytest-xdist",
   "pyyaml",
   "ruamel.yaml",
   "sympy",

pytest.ini

@@ -36,3 +36,8 @@ addopts =
     kernels/test/test_case_gen.py
     # backends/tosa
     backends/tosa/test
+
+# run the same tests multiple times to determine their
+# flakiness status. Default to 50 re-runs
+flake-finder = true
+flake-runs = 50