[test-runner] Move test case processing beyond the multi-process boundary.

tools/testrunner/local/testsuite.py

Index: tools/testrunner/local/testsuite.py
diff --git a/tools/testrunner/local/testsuite.py b/tools/testrunner/local/testsuite.py
index dd654c30350ab404a7f85dcae9851017d211b51f..5f5b218ee12d355fca93e4c78bbb01da18c7b3e9 100644
--- a/tools/testrunner/local/testsuite.py
+++ b/tools/testrunner/local/testsuite.py
@@ -88,7 +88,7 @@ class VariantGenerator(object):
 class TestSuite(object):
 
   @staticmethod
-  def LoadTestSuite(root):
+  def LoadTestSuite(root, global_init=True):
     name = root.split(os.path.sep)[-1]
     f = None
     try:
@@ -103,6 +103,8 @@ class TestSuite(object):
         f.close()
 
   def __init__(self, name, root):
+    # Note: This might be called concurrently from different processes.
+    # Changing harddisk state should be done in 'SetupWorkingDirectory' below.
     self.name = name  # string
     self.root = root  # string containing path
     self.tests = None  # list of TestCase objects
@@ -110,6 +112,11 @@ class TestSuite(object):
     self.wildcards = None  # dictionary mapping test paths to list of outcomes
     self.total_duration = None  # float, assigned on demand
 
+  def SetupWorkingDirectory(self):
+    # This is called once per test suite object in a multi-process setting.
+    # Multi-process-unsafe work-directory setup can go here.
+    pass
+
   def shell(self):
     return "d8"