Follow up to previous CL

This addresses comments from
https://dart-review.googlesource.com/c/sdk/+/58201.

Change-Id: I59fd5ea06fbd644a7ba5e6be842ce20cfaee7536
Reviewed-on: https://dart-review.googlesource.com/59060
Reviewed-by: Lasse R.H. Nielsen <lrn@google.com>
Commit-Queue: Peter von der Ahé <ahe@google.com>

pkg/analyzer/test/generated/parser_forest_test.dart

@@ -8,8 +8,8 @@ import 'package:test_reflective_loader/test_reflective_loader.dart';
 import '../src/fasta/body_builder_test_helper.dart';
 import 'parser_test.dart';
 
-main() async {
+main() {
-  await CompilerTestContext.runWithTestOptions((_) {
+  return CompilerTestContext.runWithTestOptions((_) {
     defineReflectiveSuite(() {
       defineReflectiveTests(ClassMemberParserTest_Forest);
       defineReflectiveTests(ComplexParserTest_Forest);

pkg/analyzer/test/src/fasta/body_builder_test_helper.dart

@@ -145,6 +145,13 @@ class CompilerTestContext extends CompilerContext {
 
       T result;
       Completer<T> completer = new Completer<T>();
+      // Since we're using `package:test_reflective_loader`, we can't rely on
+      // normal async behavior, as `defineReflectiveSuite` doesn't return a
+      // future. However, since it's built on top of `package:test`, we can
+      // obtain a future that completes when all the tests are done using
+      // `tearDownAll`. This allows this function to complete no earlier than
+      // when the tests are done. This is important, as we don't want to call
+      // `CompilerContext.clear` before then.
       tearDownAll(() => completer.complete(result));
       result = await action(c);
       return completer.future;

pkg/analyzer/test/src/fasta/resolution_test.dart

@@ -10,8 +10,8 @@ import 'package:test_reflective_loader/test_reflective_loader.dart';
 import '../../generated/parser_test.dart';
 import 'body_builder_test_helper.dart';
 
-main() async {
+main() {
-  await CompilerTestContext.runWithTestOptions((_) {
+  return CompilerTestContext.runWithTestOptions((_) {
     defineReflectiveSuite(() {
       defineReflectiveTests(ResolutionTest);
     });