[flutter_tool] fix incorrect coverage file generation (#71726)

packages/flutter_tools/lib/src/commands/test.dart

@@ -251,7 +251,8 @@ class TestCommand extends FlutterCommand {
         verbose: !machine,
         libraryPredicate: (String libraryName) => libraryName.contains(projectName),
         // TODO(jonahwilliams): file bug for incorrect URI handling on windows
-        packagesPath: globals.fs.path.absolute('.packages'),
+        packagesPath: globals.fs.file(buildInfo.packagesPath)
+          .parent.parent.childFile('.packages').path
       );
     }
 

packages/flutter_tools/lib/src/test/coverage_collector.dart

@@ -117,7 +117,6 @@ class CoverageCollector extends TestWatcher {
   Future<String> finalizeCoverage({
     coverage.Formatter formatter,
     Directory coverageDirectory,
-    String packagesPath,
   }) async {
     if (_globalHitmap == null) {
       return null;

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

@@ -29,6 +29,9 @@ void main() {
     await flutter.test(coverage: true);
     await flutter.done;
 
-    expect(tempDir.childDirectory('coverage').childFile('lcov.info'), exists);
+    final File lcovFile = tempDir.childDirectory('coverage').childFile('lcov.info');
+
+    expect(lcovFile, exists);
+    expect(lcovFile.readAsStringSync(), contains('main.dart')); // either 'SF:lib/main.dart or SF:lib\\main.dart
   });
 }