Explicitly determine default simulator to ensure simd is available.

Author: freakboy3742

Platforms/Apple/testbed/__main__.py

@@ -271,8 +271,14 @@ def run_testbed(
     update_test_plan(location, platform, args)
     print(" done.")
 
+    # xcodebuild doesn't guarantee that the CoreSimulatorService daemon is
+    # running prior to using a simulator, but calling `xcrun simctl list` does.
+    # Determining the default simulator that *would* be used is a cheap action;
+    # so use that as a way to ensure that the CoreSimulatorService daemon is
+    # running.
+    default_simulator = select_simulator_device(platform)
     if simulator is None:
-        simulator = select_simulator_device(platform)
+        simulator = default_simulator
     print(f"Running test on {simulator}")
 
     xcode_test(