diff --git a/fixtures/_test/pubspec.yaml b/fixtures/_test/pubspec.yaml
index 8bb81a518..51e52d58c 100644
--- a/fixtures/_test/pubspec.yaml
+++ b/fixtures/_test/pubspec.yaml
@@ -1,7 +1,11 @@
+# This code is for testing that the debugger works with weak null-safety
+# so we should not migrate it to null-safety.
+# TODO(elliette): Delete this directory post Dart 3.0 (when we no longer
+# support weak null-safety).
 name: _test
 version: 1.0.0
 description: >-
-  A fake package used for testing
+  A fake package used for testing weak null-safety.
 publish_to: none
 
 environment:
diff --git a/fixtures/_testCircular1/pubspec.yaml b/fixtures/_testCircular1/pubspec.yaml
index 69e4d87cc..f42bf6aa3 100644
--- a/fixtures/_testCircular1/pubspec.yaml
+++ b/fixtures/_testCircular1/pubspec.yaml
@@ -1,7 +1,11 @@
+# This code is for testing that the debugger works with weak null-safety
+# so we should not migrate it to null-safety.
+# TODO(elliette): Delete this directory post Dart 3.0 (when we no longer
+# support weak null-safety).
 name: _test_circular1
 version: 1.0.0
 description: >-
-  A fake package used for testing
+  A fake package used for testing weak null-safety.
 publish_to: none
 
 environment:
diff --git a/fixtures/_testCircular1Sound/pubspec.yaml b/fixtures/_testCircular1Sound/pubspec.yaml
index d5a7a9886..5b6386c18 100644
--- a/fixtures/_testCircular1Sound/pubspec.yaml
+++ b/fixtures/_testCircular1Sound/pubspec.yaml
@@ -1,11 +1,11 @@
 name: _test_circular1_sound
 version: 1.0.0
 description: >-
-  A fake package used for testing
+  A fake package used for testing sound null-safety.
 publish_to: none
 
 environment:
-  sdk: ">=2.5.0 <3.0.0"
+  sdk: '>=2.12.0 <3.0.0'
 
 dependencies:
   intl: ^0.16.0
diff --git a/fixtures/_testCircular2/pubspec.yaml b/fixtures/_testCircular2/pubspec.yaml
index 44a59a923..13f43ac70 100644
--- a/fixtures/_testCircular2/pubspec.yaml
+++ b/fixtures/_testCircular2/pubspec.yaml
@@ -1,10 +1,11 @@
+# This code is for testing that the debugger works with weak null-safety
+# so we should not migrate it to null-safety.
+# TODO(elliette): Delete this directory post Dart 3.0 (when we no longer
+# support weak null-safety).
 name: _test_circular2
 version: 1.0.0
 description: >-
-  A fake package used for testing imports. Imports _test.
-  This code is for testing that debugger works with weak null safety so we
-  should not migrate it to null safety. Once Dart 3.0 is released, we should
-  delete this directory.
+  A fake package used for testing imports with weak null-safety. Imports _test.
 publish_to: none
 
 environment:
diff --git a/fixtures/_testCircular2Sound/pubspec.yaml b/fixtures/_testCircular2Sound/pubspec.yaml
index 090859c6c..bee2c2c3d 100644
--- a/fixtures/_testCircular2Sound/pubspec.yaml
+++ b/fixtures/_testCircular2Sound/pubspec.yaml
@@ -1,14 +1,11 @@
 name: _test_circular2_sound
 version: 1.0.0
 description: >-
-  A fake package used for testing imports. Imports _test.
-  This code is for testing that debugger works with weak null safety so we
-  should not migrate it to null safety. Once Dart 3.0 is released, we should
-  delete this directory.
+  A fake package used for testing imports with sound null-safety. Imports _test.
 publish_to: none
 
 environment:
-  sdk: ">=2.10.0 <3.0.0"
+  sdk: '>=2.12.0 <3.0.0'
 
 dependencies:
   _test_circular1_sound:
diff --git a/fixtures/_testCircular2Sound/web/main.dart b/fixtures/_testCircular2Sound/web/main.dart
index d9b634a07..03fcf7969 100644
--- a/fixtures/_testCircular2Sound/web/main.dart
+++ b/fixtures/_testCircular2Sound/web/main.dart
@@ -15,5 +15,5 @@ void main() {
     testCircularDependencies();
   });
 
-  document.body.appendText(concatenate('Program', ' is running!'));
+  document.body!.appendText(concatenate('Program', ' is running!'));
 }
diff --git a/fixtures/_testPackage/pubspec.yaml b/fixtures/_testPackage/pubspec.yaml
index ace5caa3f..070e0b21f 100644
--- a/fixtures/_testPackage/pubspec.yaml
+++ b/fixtures/_testPackage/pubspec.yaml
@@ -1,10 +1,11 @@
+# This code is for testing that the debugger works with weak null-safety
+# so we should not migrate it to null-safety.
+# TODO(elliette): Delete this directory post Dart 3.0 (when we no longer
+# support weak null-safety).
 name: _test_package
 version: 1.0.0
 description: >-
-  A fake package used for testing imports. Imports _test.
-  This code is for testing that debugger works with weak null safety so we
-  should not migrate it to null safety. Once Dart 3.0 is released, we should
-  delete this directory.
+  A fake package used for testing imports with weak null-safety. Imports _test.
 publish_to: none
 
 environment:
diff --git a/fixtures/_testPackageSound/pubspec.yaml b/fixtures/_testPackageSound/pubspec.yaml
index e7c5b404d..1f30b5fca 100644
--- a/fixtures/_testPackageSound/pubspec.yaml
+++ b/fixtures/_testPackageSound/pubspec.yaml
@@ -1,7 +1,7 @@
 name: _test_package_sound
 version: 1.0.0
 description: >-
-  A fake package used for testing imports. Imports _test.
+  A fake package used for testing imports with sound null-safety. Imports _test.
 publish_to: none
 
 environment:
diff --git a/fixtures/_testSound/pubspec.yaml b/fixtures/_testSound/pubspec.yaml
index 8a3470971..438fd0eb1 100644
--- a/fixtures/_testSound/pubspec.yaml
+++ b/fixtures/_testSound/pubspec.yaml
@@ -1,7 +1,7 @@
 name: _test_sound
 version: 1.0.0
 description: >-
-  A fake package used for testing
+  A fake package used for testing sound null-safety.
 publish_to: none
 
 environment:
diff --git a/fixtures/_webdevSmoke/pubspec.yaml b/fixtures/_webdevSmoke/pubspec.yaml
index eb0e4c445..8af120f31 100644
--- a/fixtures/_webdevSmoke/pubspec.yaml
+++ b/fixtures/_webdevSmoke/pubspec.yaml
@@ -1,9 +1,10 @@
+# This code is for testing that the debugger works with weak null-safety
+# so we should not migrate it to null-safety.
+# TODO(elliette): Delete this directory post Dart 3.0 (when we no longer
+# support weak null-safety).
 name: _webdev_smoke
 description:
-  A test fixture for webdev testing.
-  This code is for testing that debugger works with weak null safety so we
-  should not migrate it to null safety. Once Dart 3.0 is released, we should
-  delete this directory.
+  A test fixture for webdev testing with weak null-safety.
 
 
 # The versions in this pubspec should match the requirements