Improves options validation type safety (#24885).

pkg/analyzer/test/src/task/options_test.dart

Index: pkg/analyzer/test/src/task/options_test.dart
diff --git a/pkg/analyzer/test/src/task/options_test.dart b/pkg/analyzer/test/src/task/options_test.dart
index 5185e9b68eb98d3bf03bf300c74b8c1bd25b5e3d..6c734c4bace0eacb9e3a832a5f912eb024544a97 100644
--- a/pkg/analyzer/test/src/task/options_test.dart
+++ b/pkg/analyzer/test/src/task/options_test.dart
@@ -93,6 +93,22 @@ analyzer:
 ''');
     expect(analysisOptions.strongMode, true);
   }
+
+  test_configure_strong_mode_bad_value() {
+    configureContext('''
+analyzer:
+  strong-mode: foo
+''');
+    expect(analysisOptions.strongMode, false);
+  }
+
+  test_configure_bad_options_contents() {
+    configureContext('''
+analyzer:
+  strong-mode:true # misformatted
+''');
+    expect(analysisOptions.strongMode, false);
+  }
 }
 
 @reflectiveTest