Tests: macOS now correctly throws unique violation exception.

Follow-up from
ccec6e8 unblock macOS CI failure

objectbox_test/test/basics_test.dart

@@ -6,7 +6,14 @@ import 'package:objectbox/src/native/bindings/helpers.dart';
 import 'package:objectbox/src/native/version.dart';
 import 'package:test/test.dart';
 
+import 'test_env.dart';
+
 void main() {
+  test("Dart version test helper", () {
+    expect(atLeastDart("2.15.0"), true);
+    expect(atLeastDart("999.0.0"), false);
+  });
+
   print("Testing basics of ObjectBox using C lib V${libraryVersion()}");
 
   // Prior to Dart 2.6, the exception wasn't accessible and may have crashed.

objectbox_test/test/box_test.dart

@@ -240,17 +240,18 @@ void main() {
       final object = TestEntity2()..value = 42;
       final future = box.putQueuedAwaitResult(object);
 
-      try {
-        await future;
-      } catch (e) {
-        // TODO: Mac in GitHub CI (not locally reproducible yet)...
-        if (Platform.isMacOS) {
-          expect(e is ObjectBoxException, isTrue);
-          expect((e as ObjectBoxException).message, '');
-        } else {
-          expect(e is UniqueViolationException, isTrue);
-          expect(e.toString(), contains('Unique constraint'));
-        }
+      if (Platform.isMacOS && !atLeastDart('3.1.0')) {
+        // Before Dart 3.1 an incorrect exception is thrown on macOS.
+        expect(
+            () async => await future,
+            throwsA(
+                predicate((e) => e is ObjectBoxException && e.message == '')));
+      } else {
+        expect(
+            () async => await future,
+            throwsA(predicate((e) =>
+                e is UniqueViolationException &&
+                e.message.contains('Unique constraint'))));
       }
 
       expect(object.id, isNull); // ID must remain unassigned

objectbox_test/test/test_env.dart

@@ -82,3 +82,14 @@ dynamic notAtLeastDart2_15_0() {
     return false;
   }
 }
+
+bool atLeastDart(String expectedLowestVersion) {
+  final dartVersion = RegExp('([0-9]+).([0-9]+).([0-9]+)')
+      .firstMatch(Platform.version)
+      ?.group(0);
+  if (dartVersion != null && dartVersion.compareTo(expectedLowestVersion) > 0) {
+    return true;
+  } else {
+    return false;
+  }
+}