Add src/diagnostics test for assert(bool?)

Change-Id: I152e279db363ceb0efdb71d5741ada4a5341b8fc
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/102521
Auto-Submit: Mike Fairhurst <mfairhurst@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
diff --git a/pkg/analyzer/test/src/diagnostics/unchecked_use_of_nullable_value_test.dart b/pkg/analyzer/test/src/diagnostics/unchecked_use_of_nullable_value_test.dart
index d008f0a..19907e9 100644
--- a/pkg/analyzer/test/src/diagnostics/unchecked_use_of_nullable_value_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/unchecked_use_of_nullable_value_test.dart
@@ -48,6 +48,24 @@
 ''');
   }
 
+  test_assert_nonNullable() async {
+    await assertNoErrorsInCode(r'''
+m() {
+  bool x = true;
+  assert(x);
+}
+''');
+  }
+
+  test_assert_nullable() async {
+    await assertErrorCodesInCode(r'''
+m() {
+  bool? x;
+  assert(x);
+}
+''', [StaticWarningCode.UNCHECKED_USE_OF_NULLABLE_VALUE]);
+  }
+
   test_await_nonNullable() async {
     await assertNoErrorsInCode(r'''
 m() async {