Run desktop darwin tests in debug mode (#21660)

diff --git a/shell/platform/darwin/macos/BUILD.gn b/shell/platform/darwin/macos/BUILD.gn
index 58a9e66..9800139 100644
--- a/shell/platform/darwin/macos/BUILD.gn
+++ b/shell/platform/darwin/macos/BUILD.gn
@@ -109,6 +109,8 @@
 
   cflags_objcc = [ "-fobjc-arc" ]
 
+  ldflags = [ "-ObjC" ]
+
   deps = [
     ":flutter_desktop_darwin_fixtures",
     ":flutter_framework_source",
diff --git a/testing/run_tests.py b/testing/run_tests.py
index a11f91c..6b2cf2f 100755
--- a/testing/run_tests.py
+++ b/testing/run_tests.py
@@ -148,6 +148,11 @@
   if IsMac():
     RunEngineExecutable(build_dir, 'flutter_channels_unittests', filter, shuffle_flags)
 
+  # These tests can only be run on Darwin on debug mode.
+  # See: https://github.com/flutter/flutter/issues/66664
+  if IsMac() and ('debug' in build_dir):
+    RunEngineExecutable(build_dir, 'flutter_desktop_darwin_unittests', filter, shuffle_flags)
+
   # https://github.com/flutter/flutter/issues/36296
   if IsLinux():
     RunEngineExecutable(build_dir, 'txt_unittests', filter, shuffle_flags)