Revert "[flutter_tool] Prevent accidental calls to io.exit when asserts are...

Revert "[flutter_tool] Prevent accidental calls to io.exit when asserts are active in unit tests (#46210)" (#46630)

This reverts commit b698c9d7.

packages/flutter_tools/lib/src/base/io.dart

@@ -26,7 +26,7 @@
 /// increase the API surface that we have to test in Flutter tools, and the APIs
 /// in `dart:io` can sometimes be hard to use in tests.
 import 'dart:async';
-import 'dart:io' as io show exit, IOSink, Platform, Process, ProcessInfo, ProcessSignal,
+import 'dart:io' as io show exit, IOSink, Process, ProcessInfo, ProcessSignal,
     stderr, stdin, Stdin, StdinException, Stdout, stdout;
 
 import 'package:meta/meta.dart';
@@ -92,26 +92,12 @@ ExitFunction _exitFunction = _defaultExitFunction;
 
 /// Exits the process.
 ///
-/// Throws [StateError] if assertions are enabled and the dart:io exit
-/// is still active when called. This may indicate exit was called in
-/// a test without being configured correctly. This behavior can be
-/// removed by setting the `FLUTTER_TEST` environment
-/// variable to a non-null string.
-///
 /// This is analogous to the `exit` function in `dart:io`, except that this
 /// function may be set to a testing-friendly value by calling
 /// [setExitFunctionForTests] (and then restored to its default implementation
 /// with [restoreExitFunction]). The default implementation delegates to
 /// `dart:io`.
-ExitFunction get exit {
-  assert(
-    _exitFunction != io.exit || io.Platform.environment['FLUTTER_TEST'] != null,
-    'io.exit was called with assertions active. If this is an integration test, '
-    'ensure that the environment variable FLUTTER_TEST is set '
-    'to a non-null String.',
-  );
-  return _exitFunction;
-}
+ExitFunction get exit => _exitFunction;
 
 /// Sets the [exit] function to a function that throws an exception rather
 /// than exiting the process; this is intended for testing purposes.

packages/flutter_tools/test/general.shard/base/io_test.dart

@@ -68,16 +68,6 @@ void main() {
   testUsingContext('ProcessSignal toString() works', () async {
     expect(io.ProcessSignal.sigint.toString(), ProcessSignal.SIGINT.toString());
   });
-
-  test('exit throws a StateError if called without being overriden', () {
-    expect(() => exit(0), throwsA(isInstanceOf<AssertionError>()));
-  });
-
-  test('exit does not throw a StateError if overriden', () {
-    setExitFunctionForTests((int value) {});
-
-    expect(() => exit(0), returnsNormally);
-  });
 }
 
 class MockIoProcessSignal extends Mock implements io.ProcessSignal {}

packages/flutter_tools/test/integration.shard/daemon_mode_test.dart

@@ -29,9 +29,6 @@ void main() {
     final Process process = await processManager.start(
       <String>[flutterBin, '--show-test-device', 'daemon'],
       workingDirectory: tempDir.path,
-      environment: <String, String>{
-        'FLUTTER_TEST': 'true',
-      }
     );
 
     final StreamController<String> stdout = StreamController<String>.broadcast();

packages/flutter_tools/test/integration.shard/test_utils.dart

@@ -46,12 +46,7 @@ Future<void> getPackages(String folder) async {
     'pub',
     'get',
   ];
-  final ProcessResult result = await processManager.run(command,
-    workingDirectory: folder,
-    environment: <String, String>{
-    'FLUTTER_TEST': 'true'
-    },
-  );
+  final ProcessResult result = await processManager.run(command, workingDirectory: folder);
   if (result.exitCode != 0) {
     throw Exception('flutter pub get failed: ${result.stderr}\n${result.stdout}');
   }