STEPS TO REPRODUCE

1. Add export FLUTTER_TOOL_ARGS=--enable-asserts to your .bashrc, or at least export it in your current shell.
2. cd dev/devicelab from your flutter/flutter checkout.
3. run flutter test.

EXPECTED RESULTS
Tests pass.

ACTUAL RESULTS
Many tests hit:

  'package:': Failed assertion: line 168 pos 16: '<optimized out>': is not true.
  [...]
  package:flutter_tools/src/test/flutter_tester_device.dart 168:16  FlutterTesterTestDevice.start.<fn>
  package:flutter_tools/src/test/flutter_tester_device.dart 359:39  FlutterTesterTestDevice._pipeStandardStreamsToConsole.<fn>
  [...]

The given line is in FlutterTesterTestDevice.start:

    _pipeStandardStreamsToConsole(
      process: _process!,
      reportVmServiceUri: (Uri detectedUri) async {
        assert(!_gotProcessVmServiceUri.isCompleted); // <-- THIS ASSERTS
        assert(debuggingOptions.hostVmServicePort == null ||
            debuggingOptions.hostVmServicePort == detectedUri.port);

I bisected this regression to #97683. cc @bkonyi