Another fix try

Author: mosuem

pubspec.yaml

@@ -11,4 +11,5 @@ dependencies:
 
 dev_dependencies:
   dart_flutter_team_lints: ^3.5.2
+  os_detect: ^2.0.3
   test: ^1.24.0

test/gzip_test.dart

@@ -3,7 +3,6 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:convert';
-import 'dart:io';
 import 'dart:typed_data';
 
 import 'package:gzip/gzip.dart';
@@ -36,14 +35,6 @@ void main() {
   }
 }
 
-final osHeader = Platform.isLinux
-    ? 3
-    : Platform.isMacOS
-    ? 19
-    : Platform.isWindows
-    ? 10
-    : -1;
-
 final cases = [
   (
     name: 'Simple ASCII',
@@ -58,7 +49,7 @@ final cases = [
       0,
       0,
       0,
-      osHeader,
+      3,
       243,
       72,
       205,
@@ -95,7 +86,7 @@ final cases = [
       0,
       0,
       0,
-      osHeader,
+      3,
       1,
       55,
       0,

test/helper_web.dart

@@ -4,4 +4,20 @@
 
 import 'dart:typed_data';
 
-Uint8List switchPlatformBit(List<int> input) => Uint8List.fromList(input);
+import 'package:os_detect/os_detect.dart';
+
+Uint8List switchPlatformBit(List<int> input) {
+  const osBit = 9;
+  if (operatingSystemVersion.contains('linux')) {
+    input[osBit] = 3;
+  } else if (operatingSystemVersion.contains('macos')) {
+    input[osBit] = 19;
+  } else if (operatingSystemVersion.contains('windows')) {
+    input[osBit] = 10;
+  } else {
+    throw UnimplementedError(
+      'No OS bit for platform $operatingSystemVersion found',
+    );
+  }
+  return Uint8List.fromList(input);
+}