fix(test_core): fix writeCoverage to handle a null hit map

pkgs/test/CHANGELOG.md

@@ -1,5 +1,6 @@
 ## 1.27.1-wip
 
+* Bump `test_core` to 0.6.14
 * Removed unused `js` dependency
 
 ## 1.27.0

pkgs/test/pubspec.yaml

@@ -36,7 +36,7 @@ dependencies:
 
   # Use an exact version until the test_api and test_core package are stable.
   test_api: 0.7.8
-  test_core: 0.6.13
+  test_core: 0.6.14
 
   typed_data: ^1.3.0
   web_socket_channel: '>=2.0.0 <4.0.0'

pkgs/test_core/CHANGELOG.md

@@ -1,3 +1,7 @@
+## 0.6.14
+
+* Fix type cast when parsing a `null` hit map.
+
 ## 0.6.13
 
 * Require Dart 3.7

pkgs/test_core/lib/src/runner/coverage.dart

@@ -30,7 +30,16 @@ Future<Coverage> writeCoverage(
     await out.flush();
     await out.close();
   }
-  return HitMap.parseJson(coverage['coverage'] as List<Map<String, dynamic>>);
+  return switch (coverage['coverage']) {
+    // Matching on `List<dynamic>` the runtime type of `List` in JSON is
+    // never `Map<String, dynamic>`. The `cast` below ensures the runtime type
+    // is correct for `HitMap.parseJson`.
+    List<dynamic> hitMapJson => HitMap.parseJson(
+      hitMapJson.cast<Map<String, dynamic>>(),
+    ),
+    null => const {},
+    _ => throw StateError('Invalid coverage data'),
+  };
 }
 
 Future<void> writeCoverageLcov(

pkgs/test_core/pubspec.yaml

@@ -1,5 +1,5 @@
 name: test_core
-version: 0.6.13
+version: 0.6.14
 description: A basic library for writing tests and running them on the VM.
 repository: https://github.com/dart-lang/test/tree/master/pkgs/test_core
 issue_tracker: https://github.com/dart-lang/test/issues?q=is%3Aissue+is%3Aopen+label%3Apackage%3Atest