Repository: flutter
Issue: Flutter framework tests fail when run with high -j
Labels: a: tests,team,tool,framework,P3,team-framework,triaged-framework

If I run `flutter test -j10` on my 20-core machine, everything's fine; it takes about 3 minutes, could be faster, but it runs fine.

If I run `flutter test -j60`, it works fine at first, and then after a while a bunch of tests fail with things like:

```
01:33 +5464 ~15 -146: loading /home/ianh/dev/flutter/packages/flutter/test/cupertino/segmented_control_test.dart [E]
  Failed to load "/home/ianh/dev/flutter/packages/flutter/test/cupertino/segmented_control_test.dart":
  ^E
    Command: /home/ianh/dev/flutter/bin/cache/artifacts/engine/linux-x64/flutter_tester --disable-observatory --enable-checked-mode --verify-entry-points --enable-software-rendering -\
-skia-deterministic-rendering --enable-dart-profiling --non-interactive --use-test-fonts --packages=/home/ianh/dev/flutter/packages/flutter/.dart_tool/package_config.json /tmp/flutter\
_tools.ZINKVV/flutter_test_listener.OWDOYQ/listener.dart.dill
01:33 +5466 ~15 -147: loading /home/ianh/dev/flutter/packages/flutter/test/cupertino/switch_test.dart [E]
  Failed to load "/home/ianh/dev/flutter/packages/flutter/test/cupertino/switch_test.dart":
  ^E
    Command: /home/ianh/dev/flutter/bin/cache/artifacts/engine/linux-x64/flutter_tester --disable-observatory --enable-checked-mode --verify-entry-points --enable-software-rendering -\
-skia-deterministic-rendering --enable-dart-profiling --non-interactive --use-test-fonts --packages=/home/ianh/dev/flutter/packages/flutter/.dart_tool/package_config.json /tmp/flutter\
_tools.ZINKVV/flutter_test_listener.HLAZLY/listener.dart.dill
01:33 +5466 ~15 -148: loading /home/ianh/dev/flutter/packages/flutter/test/cupertino/text_field_restoration_test.dart [E]
  Failed to load "/home/ianh/dev/flutter/packages/flutter/test/cupertino/text_field_restoration_test.dart":
  ^E
    Command: /home/ianh/dev/flutter/bin/cache/artifacts/engine/linux-x64/flutter_tester --disable-observatory --enable-checked-mode --verify-entry-points --enable-software-rendering -\
-skia-deterministic-rendering --enable-dart-profiling --non-interactive --use-test-fonts --packages=/home/ianh/dev/flutter/packages/flutter/.dart_tool/package_config.json /tmp/flutter\
_tools.ZINKVV/flutter_test_listener.UMFTXZ/listener.dart.dill
01:33 +5478 ~15 -149: loading /home/ianh/dev/flutter/packages/flutter/test/cupertino/nav_bar_test.dart [E]
  Failed to load "/home/ianh/dev/flutter/packages/flutter/test/cupertino/nav_bar_test.dart":
  ^E
    Command: /home/ianh/dev/flutter/bin/cache/artifacts/engine/linux-x64/flutter_tester --disable-observatory --enable-checked-mode --verify-entry-points --enable-software-rendering -\
-skia-deterministic-rendering --enable-dart-profiling --non-interactive --use-test-fonts --packages=/home/ianh/dev/flutter/packages/flutter/.dart_tool/package_config.json /tmp/flutter\
_tools.ZINKVV/flutter_test_listener.ZSUTWW/listener.dart.dill
01:33 +5487 ~15 -150: loading /home/ianh/dev/flutter/packages/flutter/test/cupertino/page_test.dart [E]
  Failed to load "/home/ianh/dev/flutter/packages/flutter/test/cupertino/page_test.dart":
  ^E
    Command: /home/ianh/dev/flutter/bin/cache/artifacts/engine/linux-x64/flutter_tester --disable-observatory --enable-checked-mode --verify-entry-points --enable-software-rendering -\
-skia-deterministic-rendering --enable-dart-profiling --non-interactive --use-test-fonts --packages=/home/ianh/dev/flutter/packages/flutter/.dart_tool/package_config.json /tmp/flutter\
_tools.ZINKVV/flutter_test_listener.VSGHEY/listener.dart.dill
01:34 +5500 ~15 -151: loading /home/ianh/dev/flutter/packages/flutter/test/cupertino/tab_test.dart [E]
  Failed to load "/home/ianh/dev/flutter/packages/flutter/test/cupertino/tab_test.dart":
  ^E
    Command: /home/ianh/dev/flutter/bin/cache/artifacts/engine/linux-x64/flutter_tester --disable-observatory --enable-checked-mode --verify-entry-points --enable-software-rendering -\
-skia-deterministic-rendering --enable-dart-profiling --non-interactive --use-test-fonts --packages=/home/ianh/dev/flutter/packages/flutter/.dart_tool/package_config.json /tmp/flutter\
_tools.ZINKVV/flutter_test_listener.INSAOU/listener.dart.dill
01:34 +5535 ~15 -152: loading /home/ianh/dev/flutter/packages/flutter/test/cupertino/context_menu_test.dart [E]
  Failed to load "/home/ianh/dev/flutter/packages/flutter/test/cupertino/context_menu_test.dart":
  H-^G^\7^?
    Command: /home/ianh/dev/flutter/bin/cache/artifacts/engine/linux-x64/flutter_tester --disable-observatory --enable-checked-mode --verify-entry-points --enable-software-rendering -\
-skia-deterministic-rendering --enable-dart-profiling --non-interactive --use-test-fonts --packages=/home/ianh/dev/flutter/packages/flutter/.dart_tool/package_config.json /tmp/flutter\
_tools.ZINKVV/flutter_test_listener.UEQSQI/listener.dart.dill
01:34 +5540 ~15 -153: loading /home/ianh/dev/flutter/packages/flutter/test/scheduler/benchmarks_test.dart [E]
  Failed to load "/home/ianh/dev/flutter/packages/flutter/test/scheduler/benchmarks_test.dart":
  H-^G^\7^?
    Command: /home/ianh/dev/flutter/bin/cache/artifacts/engine/linux-x64/flutter_tester --disable-observatory --enable-checked-mode --verify-entry-points --enable-software-rendering -\
-skia-deterministic-rendering --enable-dart-profiling --non-interactive --use-test-fonts --packages=/home/ianh/dev/flutter/packages/flutter/.dart_tool/package_config.json /tmp/flutter\
_tools.ZINKVV/flutter_test_listener.HOGPBH/listener.dart.dill
01:35 +5540 ~15 -154: loading /home/ianh/dev/flutter/packages/flutter/test/scheduler/debug_test.dart [E]
  Failed to load "/home/ianh/dev/flutter/packages/flutter/test/scheduler/debug_test.dart":
  H-^G^\7^?
    Command: /home/ianh/dev/flutter/bin/cache/artifacts/engine/linux-x64/flutter_tester --disable-observatory --enable-checked-mode --verify-entry-points --enable-software-rendering -\
-skia-deterministic-rendering --enable-dart-profiling --non-interactive --use-test-fonts --packages=/home/ianh/dev/flutter/packages/flutter/.dart_tool/package_config.json /tmp/flutter\
_tools.ZINKVV/flutter_test_listener.XVTCUC/listener.dart.dill
```

Presumably there's some kind of race condition that kicks in when you are running more than one test-per-available-core or some such.