diff --git a/packages/fl_query/lib/src/core/models.dart b/packages/fl_query/lib/src/core/models.dart
index c7c3b0d..2abc42c 100644
--- a/packages/fl_query/lib/src/core/models.dart
+++ b/packages/fl_query/lib/src/core/models.dart
@@ -120,7 +120,7 @@ class QueryFilters {
   bool? exact;
   bool? inactive;
   bool Function(Query query)? predicate;
-  bool? queryKey;
+  QueryKey? queryKey;
   bool? stale;
   bool? fetching;
 
@@ -162,7 +162,7 @@ class RefetchableQueryFilters<TPageData> extends QueryFilters
     bool? exact,
     bool? inactive,
     bool Function(Query query)? predicate,
-    bool? queryKey,
+    QueryKey? queryKey,
     bool? stale,
     bool? fetching,
     this.refetchPage,
@@ -212,7 +212,7 @@ class InvalidateQueryFilters<TPageData>
     bool? exact,
     bool? inactive,
     bool Function(Query query)? predicate,
-    bool? queryKey,
+    QueryKey? queryKey,
     bool? stale,
     bool? fetching,
     bool Function(TPageData lastPage, int index, List<TPageData> allPages)?
@@ -452,6 +452,11 @@ class QueryObserverOptions<
     QueryMeta? meta,
     bool? structuralSharing,
     bool? defaulted,
+    ShouldRetryFunction<TError>? retry,
+    RetryDelayFunction<TError>? retryDelay,
+    QueryBehavior<TQueryFnData, TError, TQueryData>? behavior,
+    GetPreviousPageParamFunction<TQueryFnData>? getPreviousPageParam,
+    GetNextPageParamFunction<TQueryFnData>? getNextPageParam,
   }) : super(
           queryKey: queryKey,
           queryKeyHashFn: queryKeyHashFn,
@@ -464,6 +469,11 @@ class QueryObserverOptions<
           meta: meta,
           structuralSharing: structuralSharing,
           defaulted: defaulted,
+          behavior: behavior,
+          getNextPageParam: getNextPageParam,
+          getPreviousPageParam: getPreviousPageParam,
+          retry: retry,
+          retryDelay: retryDelay,
         );
 
   QueryObserverOptions.fromJson(Map<String, dynamic> json)
diff --git a/packages/fl_query/lib/src/core/query.dart b/packages/fl_query/lib/src/core/query.dart
index 7da3e25..8223f23 100644
--- a/packages/fl_query/lib/src/core/query.dart
+++ b/packages/fl_query/lib/src/core/query.dart
@@ -1,4 +1,6 @@
 import 'dart:async';
+import 'dart:collection';
+import 'dart:convert';
 import 'dart:math';
 
 import 'package:fl_query/src/core/models.dart';
@@ -280,7 +282,9 @@ class Query<TQueryFnData extends Map<String, dynamic>, TError,
         data = prevData as TData;
       } else if (this.options.structuralSharing != false) {
         // Structurally share data between prev and new data if needed
-        data = replaceEqualDeep(prevData, data);
+        final merged =
+            Map<String, dynamic>.from(replaceEqualDeep(prevData, data));
+        data = merged as TData;
       }
       // Set data and mark it as cached
       _dispatch(Action(
@@ -360,7 +364,7 @@ class Query<TQueryFnData extends Map<String, dynamic>, TError,
     // Use the options from the first observer with a query function if no function is found.
     // This can happen when the query is hydrated or created with setQueryData.
     if (this.options.queryFn == null) {
-      var observer =
+      final observer =
           _observers.firstWhereOrNull((x) => x.options.queryFn != null);
       if (observer != null) {
         _setOptions(QueryOptions<TQueryFnData, TError, TData>(
diff --git a/packages/fl_query/lib/src/core/query_cache.dart b/packages/fl_query/lib/src/core/query_cache.dart
index 4f5f4a7..0775ce0 100644
--- a/packages/fl_query/lib/src/core/query_cache.dart
+++ b/packages/fl_query/lib/src/core/query_cache.dart
@@ -171,7 +171,7 @@ class QueryCache extends Subscribable<QueryCacheListener> {
 
   void notify(QueryCacheNotifyEvent event) {
     notifyManager.batch(() {
-      for (var listener in listeners) {
+      for (final listener in listeners) {
         listener(event);
       }
     });
diff --git a/packages/fl_query/lib/src/core/query_client.dart b/packages/fl_query/lib/src/core/query_client.dart
index ecfed27..3f8e47b 100644
--- a/packages/fl_query/lib/src/core/query_client.dart
+++ b/packages/fl_query/lib/src/core/query_client.dart
@@ -266,7 +266,7 @@ class QueryClient {
     QueryFunction<TQueryFnData, dynamic>? queryFn,
     FetchQueryOptions<TQueryFnData, TError, TData>? options,
   }) {
-    var defaultedOptions = this.defaultQueryOptions(
+    final defaultedOptions = this.defaultQueryOptions(
       QueryObserverOptions<Map<String, dynamic>, dynamic, Map<String, dynamic>,
           TData>(
         queryFn: queryFn,
@@ -285,7 +285,7 @@ class QueryClient {
     );
     // returning 0 indicates turing off retry
     defaultedOptions.retry ??= (_, __) => 0;
-    var query = _queryCache.build<Map<String, dynamic>, dynamic, TData>(
+    final query = _queryCache.build<Map<String, dynamic>, dynamic, TData>(
         this, defaultedOptions);
     return query.isStaleByTime(defaultedOptions.staleTime)
         ? query.fetch(defaultedOptions)
@@ -313,7 +313,7 @@ class QueryClient {
           TQueryData extends Map<String, dynamic>>(
       QueryObserverOptions<TQueryFnData, TError, TData, TQueryData>? options) {
     if (options?.defaulted == true) return options!;
-    var defaultedOptions =
+    final defaultedOptions =
         QueryObserverOptions<TQueryFnData, TError, TData, TQueryData>.fromJson({
       ...(_defaultOptions.queries?.toJson() ?? {}),
       ...(getQueryDefaults(options?.queryKey)?.toJson() ?? {}),
diff --git a/packages/fl_query/lib/src/core/query_observer.dart b/packages/fl_query/lib/src/core/query_observer.dart
index 7ecc37a..5c1acf0 100644
--- a/packages/fl_query/lib/src/core/query_observer.dart
+++ b/packages/fl_query/lib/src/core/query_observer.dart
@@ -94,6 +94,9 @@ class QueryObserver<
   Timer? _refetchInterval;
   Duration? _currentRefetchInterval;
 
+  @protected
+  Timer? get refetchInterval => _refetchInterval;
+
   QueryObserver(
     this._client,
     QueryObserverOptions<TQueryFnData, TError, TData, TQueryData>? _options,
@@ -225,9 +228,9 @@ class QueryObserver<
     throw UnimplementedError("COULD NOT IMPLEMENT DUE TO LANGUAGE LIMITATIONS");
   }
 
-  Future<QueryObserverResult<TData, TError>> getNextResult(
+  Future<QueryObserverResult<TData, TError>> getNextResult([
     bool? throwOnError,
-  ) {
+  ]) {
     final completer = Completer<QueryObserverResult<TData, TError>>();
     var unsubscribe;
     unsubscribe = subscribe((result) {
@@ -445,7 +448,8 @@ class QueryObserver<
         try {
           data = options.select?.call(state.data);
           if (options.structuralSharing != false) {
-            data = replaceEqualDeep(prevResult?.data, data);
+            data = Map<String, dynamic>.from(
+                replaceEqualDeep(prevResult?.data, data)) as TData;
           }
           if (options.select != null && data != null) {
             _previousSelect = SelectQuery<TQueryData, TData>(
diff --git a/packages/fl_query/test/helpers/utils.dart b/packages/fl_query/test/helpers/utils.dart
index b56c6c3..9a73ba2 100644
--- a/packages/fl_query/test/helpers/utils.dart
+++ b/packages/fl_query/test/helpers/utils.dart
@@ -6,3 +6,46 @@ Uuid uuid = Uuid();
 QueryKey queryKey() {
   return QueryKey("query_${uuid.v4()}");
 }
+
+class SpyFn<T extends Function()> {
+  int _calls = 0;
+  late T _customFn;
+  int get calls => _calls;
+  T get customFn => _customFn;
+
+  SpyFn();
+
+  SpyFn.withFn(this._customFn);
+
+  fn([Function()? cb]) {
+    _calls++;
+    return () => cb?.call();
+  }
+
+  fn1([Function()? cb]) {
+    _calls++;
+    return (p0) => cb?.call();
+  }
+
+  fn2([Function()? cb]) {
+    _calls++;
+    return (p0, p1) => cb?.call();
+  }
+
+  fn3([Function()? cb]) {
+    _calls++;
+    return (p0, p1, p2) => cb?.call();
+  }
+
+  fn4([Function()? cb]) {
+    _calls++;
+    return (p0, p1, p2, p3) => cb?.call();
+  }
+
+  fn5([Function()? cb]) {
+    _calls++;
+    return (p0, p1, p2, p3, p4) => cb?.call();
+  }
+}
+
+Future<void> sleep(int ms) => Future.delayed(Duration(milliseconds: ms));
diff --git a/packages/fl_query/test/src/core/query_observer_test.dart b/packages/fl_query/test/src/core/query_observer_test.dart
index 1764feb..c5a2068 100644
--- a/packages/fl_query/test/src/core/query_observer_test.dart
+++ b/packages/fl_query/test/src/core/query_observer_test.dart
@@ -1,8 +1,14 @@
+import 'dart:async';
+
 import 'package:fl_query/src/core/core.dart';
+import 'package:fl_query/src/core/query_observer.dart';
 import 'package:test/test.dart';
 
 import '../../helpers/utils.dart';
 
+typedef QueryFn = FutureOr<Map<String, dynamic>> Function(
+    QueryFunctionContext<dynamic>);
+
 void main() {
   group('QueryObserver', () {
     late QueryClient queryClient;
@@ -18,6 +24,7 @@ void main() {
 
     test('should trigger a fetch when subscribed', () async {
       final key = queryKey();
+      ;
       int calls = 0;
       queryFn(context) {
         calls++;
@@ -64,5 +71,839 @@ void main() {
       expect(results[3].data, {"data": 2});
       expect(results[3].status, QueryStatus.success);
     });
+
+    test('should be able to fetch with a selector', () async {
+      final key = queryKey();
+      ;
+      final observer = QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: (_) => {"count": 1},
+            select: (data) => ({"myCount": data?["count"]}),
+          ));
+      QueryObserverResult? observerResult;
+      final unsubscribe = observer.subscribe((result) {
+        observerResult = result;
+      });
+      await Future.delayed(Duration(milliseconds: 1));
+      unsubscribe();
+      expect(
+        observerResult?.data,
+        equals({"myCount": 1}),
+      );
+    });
+
+    test('should be able to fetch with a selector using the fetch method',
+        () async {
+      final key = queryKey();
+      ;
+      final observer = QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: (_) => {"count": 1},
+            select: (data) => ({"myCount": data?["count"]}),
+          ));
+      final observerResult = await observer.refetch();
+      expect(observerResult?.data, equals({"myCount": 1}));
+    });
+
+    test('should run the selector again if the data changed', () async {
+      final key = queryKey();
+      ;
+      int count = 0;
+      final observer = QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: (_) => Map.from({"count": count}),
+            select: (data) {
+              count++;
+              return Map.from({"myCount": data?["count"]});
+            },
+          ));
+      final observerResult1 = await observer.refetch();
+      final observerResult2 = await observer.refetch();
+      expect(count, 2);
+      expect(observerResult1?.data, equals({"myCount": 0}));
+      expect(observerResult2?.data, equals({"myCount": 1}));
+    });
+
+    test('should run the selector again if the selector changed', () async {
+      final key = queryKey();
+      ;
+      int count = 0;
+      final List<QueryObserverResult> results = [];
+      final queryFn = (_) => ({"count": 1});
+      select1(data) {
+        count++;
+        return {"myCount": data?["count"]};
+      }
+
+      select2(_data) {
+        count++;
+        return {"myCount": 99};
+      }
+
+      final observer = new QueryObserver(
+          queryClient,
+          QueryObserverOptions(
+            queryKey: key,
+            queryFn: queryFn,
+            select: select1,
+          ));
+      final unsubscribe = observer.subscribe((result) {
+        results.add(result);
+      });
+      await Future.delayed(Duration(milliseconds: 1));
+      observer.setOptions(QueryObserverOptions(
+        queryKey: key,
+        queryFn: queryFn,
+        select: select2,
+      ));
+      await Future.delayed(Duration(milliseconds: 1));
+      await observer.refetch();
+      unsubscribe();
+      expect(count, 2);
+      expect(results.length, 5);
+      expect(results.first.status, QueryStatus.loading);
+      expect(results.first.isFetching, isTrue);
+      expect(results.first.data, isNull);
+      expect(results[1].status, QueryStatus.success);
+      expect(results[1].isFetching, false);
+      expect(results[1].data, {"myCount": 1});
+      expect(results[2].status, QueryStatus.success);
+      expect(results[2].isFetching, false);
+      expect(results[2].data, {"myCount": 99});
+      expect(results[3].status, QueryStatus.success);
+      expect(results[3].isFetching, true);
+      expect(results[3].data, {"myCount": 99});
+      expect(results.last.status, QueryStatus.success);
+      expect(results.last.isFetching, false);
+      expect(results.last.data, {"myCount": 99});
+    });
+    test(
+        'should not run the selector again if the data and selector did not change',
+        () async {
+      final key = queryKey();
+      ;
+      int count = 0;
+      final List<QueryObserverResult> results = [];
+      final queryFn = (_) => {"count": 1};
+      select(data) {
+        count++;
+        return {"myCount": data["count"]};
+      }
+
+      final observer = new QueryObserver(
+          queryClient,
+          QueryObserverOptions(
+            queryKey: key,
+            queryFn: queryFn,
+            select: select,
+          ));
+      final unsubscribe = observer.subscribe((result) {
+        results.add(result);
+      });
+      await Future.delayed(Duration(milliseconds: 1));
+      observer.setOptions(QueryObserverOptions(
+        queryKey: key,
+        queryFn: queryFn,
+        select: select,
+      ));
+      await Future.delayed(Duration(milliseconds: 1));
+      await observer.refetch();
+      unsubscribe();
+      expect(count, 1);
+      expect(results.length, 4);
+      expect(results.first.status, QueryStatus.loading);
+      expect(results.first.isFetching, isTrue);
+      expect(results.first.data, isNull);
+      expect(results[1].status, QueryStatus.success);
+      expect(results[1].isFetching, false);
+      expect(results[1].data, {"myCount": 1});
+      expect(results[2].status, QueryStatus.success);
+      expect(results[2].isFetching, true);
+      expect(results[2].data, {"myCount": 1});
+      expect(results.last.status, QueryStatus.success);
+      expect(results.last.isFetching, false);
+      expect(results.last.data, {"myCount": 1});
+    });
+
+    test('should not run the selector again if the data did not change',
+        () async {
+      final key = queryKey();
+      ;
+      int count = 0;
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+          Map<String, dynamic>, Map<String, dynamic>>(
+        queryClient,
+        QueryObserverOptions<Map<String, dynamic>, dynamic,
+            Map<String, dynamic>, Map<String, dynamic>>(
+          queryKey: key,
+          queryFn: (_) => {"count": count},
+          select: (data) {
+            count++;
+            return {"myCount": data?["count"]};
+          },
+        ),
+      );
+      final observerResult1 = await observer.refetch();
+      final observerResult2 = await observer.refetch();
+      expect(count, 1);
+      expect(observerResult1?.data, equals({"myCount": 1}));
+      expect(observerResult2?.data, equals({"myCount": 1}));
+    });
+
+    test('should always run the selector again if selector throws an error',
+        () async {
+      final key = queryKey();
+      ;
+      final List<QueryObserverResult> results = [];
+      select(data) {
+        throw new Exception('selector error');
+      }
+
+      queryFn(_) => ({"count": 1});
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: queryFn,
+            select: select,
+          ));
+      final unsubscribe = observer.subscribe((result) {
+        results.add(result);
+      });
+      await Future.delayed(Duration(milliseconds: 1));
+      await observer.refetch();
+      unsubscribe();
+      expect(results.length, 5);
+      expect(results.first.status, QueryStatus.loading);
+      expect(results.first.isFetching, isTrue);
+      expect(results.first.data, isNull);
+      expect(results[1].status, QueryStatus.error);
+      expect(results[1].isFetching, false);
+      expect(results[1].data, isNull);
+      expect(results[2].status, QueryStatus.error);
+      expect(results[2].isFetching, true);
+      expect(results[2].data, isNull);
+      expect(results[3].status, QueryStatus.error);
+      expect(results[3].isFetching, false);
+      expect(results[3].data, isNull);
+      expect(results.last.status, QueryStatus.error);
+      expect(results.last.isFetching, false);
+      expect(results.last.data, isNull);
+    });
+
+    test('should structurally share the selector', () async {
+      final key = queryKey();
+      ;
+      int count = 0;
+      final observer = new QueryObserver(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: (_) => {"count": ++count},
+            select: (data) {
+              return {"myCount": 1};
+            },
+          ));
+      final observerResult1 = await observer.refetch();
+      final observerResult2 = await observer.refetch();
+      expect(count, 2);
+      expect(observerResult1?.data, isNotNull);
+      expect(observerResult1?.data, equals(observerResult2?.data));
+    });
+
+    test('should not trigger a fetch when subscribed and disabled', () async {
+      int count = 0;
+      final key = queryKey();
+      ;
+      final observer = new QueryObserver(
+          queryClient,
+          QueryObserverOptions(
+            queryKey: key,
+            queryFn: (_) {
+              count++;
+              return {"data": null};
+            },
+            enabled: false,
+          ));
+      final unsubscribe = observer.subscribe();
+      await Future.delayed(Duration(milliseconds: 1));
+      unsubscribe();
+      expect(count, 0);
+    });
+
+    test('should not trigger a fetch when not subscribed', () async {
+      int count = 0;
+      final key = queryKey();
+      ;
+      new QueryObserver(
+          queryClient,
+          QueryObserverOptions(
+            queryKey: key,
+            queryFn: (_) {
+              count++;
+              return {"data": null};
+            },
+          ));
+      await Future.delayed(Duration(milliseconds: 1));
+      expect(count, 0);
+    });
+
+    test('should be able to watch a query without defining a query function',
+        () async {
+      int count = 0;
+      int subscribeCount = 0;
+      final key = queryKey();
+      ;
+      queryFn(_) {
+        count++;
+        return {"data": null};
+      }
+
+      final observer = QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: queryFn,
+            enabled: false,
+          ));
+
+      final unsubscribe = observer.subscribe((_) {
+        subscribeCount++;
+      });
+      await queryClient.fetchQuery(queryKey: key, queryFn: queryFn);
+      unsubscribe();
+      expect(count, 1);
+      expect(subscribeCount, 2);
+    });
+
+    test('should accept unresolved query config in update function', () async {
+      final key = queryKey();
+      ;
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            enabled: false,
+          ));
+
+      final List<QueryObserverResult> results = [];
+      final unsubscribe = observer.subscribe((x) {
+        results.add(x);
+      });
+      observer.setOptions(
+        QueryObserverOptions(
+          enabled: false,
+          staleTime: Duration(milliseconds: 10),
+        ),
+      );
+      int count = 0;
+
+      queryFn(_) {
+        count++;
+        return {"data": null};
+      }
+
+      await queryClient.fetchQuery(queryKey: key, queryFn: queryFn);
+      await Future.delayed(Duration(milliseconds: 100));
+      unsubscribe();
+      expect(count, 1);
+      expect(results.length, 3);
+      expect(results[0].isStale, true);
+      expect(results[1].isStale, false);
+      expect(results[2].isStale, true);
+    });
+
+    test('should be able to handle multiple subscribers', () async {
+      final key = queryKey();
+
+      int count = 0;
+
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            enabled: false,
+          ));
+      final List<QueryObserverResult> results1 = [];
+      final List<QueryObserverResult> results2 = [];
+      final unsubscribe1 = observer.subscribe((x) {
+        results1.add(x);
+      });
+      final unsubscribe2 = observer.subscribe((x) {
+        results2.add(x);
+      });
+      await queryClient
+          .fetchQuery<Map<String, dynamic>, dynamic, Map<String, dynamic>>(
+        queryKey: key,
+        queryFn: (_) {
+          count++;
+          return {"data": false};
+        },
+      );
+      await sleep(50);
+      unsubscribe1();
+      unsubscribe2();
+      expect(count, 1);
+      expect(results1.length, 2);
+      expect(results2.length, 2);
+      expect(results1[0].data?["data"], isNull);
+      expect(results1[1].data?["data"], isFalse);
+      expect(results2[0].data?["data"], isNull);
+      expect(results2[1].data?["data"], isFalse);
+    });
+
+    test('should be able to resolve a promise', () async {
+      final key = queryKey();
+      int count = 0;
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            enabled: false,
+          ));
+      QueryObserverResult<Map<String, dynamic>, dynamic>? value;
+      observer.getNextResult().then((x) {
+        value = x;
+      });
+      queryClient
+          .prefetchQuery<Map<String, dynamic>, dynamic, Map<String, dynamic>>(
+              queryKey: key,
+              queryFn: (_) {
+                count++;
+                return {"data": "a data"};
+              });
+      await sleep(50);
+      expect(count, 1);
+      expect(value?.data?["data"], "a data");
+    });
+
+    test('should be able to resolve a promise with an error', () async {
+      final key = queryKey();
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            enabled: false,
+          ));
+      var error;
+      observer.getNextResult(true).catchError((e) {
+        error = e;
+      });
+      queryClient
+          .prefetchQuery<Map<String, dynamic>, dynamic, Map<String, dynamic>>(
+              queryKey: key, queryFn: (_) => Future.error('reject'));
+      await sleep(50);
+      expect(error, 'reject');
+    });
+
+    test('should stop retry when unsubscribing', () async {
+      final key = queryKey();
+      int count = 0;
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+          Map<String, dynamic>, Map<String, dynamic>>(
+        queryClient,
+        QueryObserverOptions<Map<String, dynamic>, dynamic,
+            Map<String, dynamic>, Map<String, dynamic>>(
+          queryKey: key,
+          queryFn: (_) {
+            count++;
+            return Future.error({"data": 'reject'});
+          },
+          retry: (_, __) => 10,
+          retryDelay: (_, __) => 50,
+        ),
+      );
+      final unsubscribe = observer.subscribe();
+      await sleep(70);
+      unsubscribe();
+      await sleep(200);
+      expect(count, 2);
+    });
+
+    test('should clear interval when unsubscribing to a refetchInterval query',
+        () async {
+      final key = queryKey();
+
+      final fetchData =
+          (_) => Future<Map<String, dynamic>>.error({'data': null});
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: fetchData,
+            cacheTime: Duration.zero,
+            refetchInterval: (_, __) => Duration(milliseconds: 1),
+          ));
+      final unsubscribe = observer.subscribe();
+      // @ts-expect-error
+      expect(observer.refetchInterval, isNull);
+      unsubscribe();
+      // @ts-expect-error
+      expect(observer.refetchInterval, isNotNull);
+      await sleep(10);
+      expect(queryClient.getQueryCache().find(key), isNotNull);
+    });
+
+    test(
+        'uses placeholderData as non-cache data when loading a query with no data',
+        () async {
+      final key = queryKey();
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: (_) => {'data': 'data'},
+            placeholderData: {"data": 'placeholder'},
+          ));
+      final result = observer.getCurrentResult();
+      expect(result?.status, QueryStatus.success);
+
+      final List<QueryObserverResult> results = [];
+
+      final unsubscribe = observer.subscribe((x) {
+        results.add(x);
+      });
+
+      await sleep(10);
+      unsubscribe();
+
+      expect(results.length, 2);
+      expect(results.first.status, QueryStatus.success);
+      expect(results.first.data, equals({"data": 'placeholder'}));
+      expect(results.last.status, QueryStatus.success);
+      expect(results.last.data, equals({'data': 'data'}));
+    });
+
+    test(
+        'the retryer should not throw an error when reject if the retrier is already resolved',
+        () async {
+      final key = queryKey();
+      int count = 0;
+
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: (_) {
+              count++;
+              return Future.error({'reject': count});
+            },
+            retry: (_, __) => 1,
+            retryDelay: (_, __) => 20,
+          ));
+
+      final unsubscribe = observer.subscribe();
+
+      // Simulate a race condition when an unsubscribe and a retry occur.
+      await sleep(20);
+      unsubscribe();
+
+      // A second reject is triggered for the retry
+      // but the retryer has already set isResolved to true
+      // so it does nothing and no error is thrown
+
+      // Should not log an error
+      queryClient.clear();
+      await sleep(40);
+      expect(true, true);
+      // expect(consoleMock).not.toHaveBeenNthCalledWith(1, 'reject 1')
+
+      // consoleMock.mockRestore()
+    });
+
+    test('getCurrentQuery should return the current query', () async {
+      final key = queryKey();
+
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+                  Map<String, dynamic>, Map<String, dynamic>>(
+              queryKey: key, queryFn: (_) => {'data': 'data'}));
+
+      expect(observer.getCurrentQuery().queryKey, key);
+    });
+
+    test('should throw an error if throwOnError option is true', () async {
+      final key = queryKey();
+
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: (_) => Future.error({'error': 'error'}),
+            retry: (_, __) => 0,
+          ));
+
+      var error = null;
+      try {
+        await observer.refetch(options: RefetchOptions(throwOnError: true));
+      } catch (err) {
+        error = err;
+      }
+
+      expect(error, equals({'error': 'error'}));
+    });
+
+    test(
+        'should not refetch in background if refetchIntervalInBackground is false',
+        () async {
+      final key = queryKey();
+      final spy = SpyFn();
+
+      // focusManager.setFocused(false)
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: spy.fn1(),
+            refetchIntervalInBackground: false,
+            refetchInterval: (_, __) => Duration(milliseconds: 10),
+          ));
+
+      final unsubscribe = observer.subscribe();
+      await sleep(30);
+
+      expect(spy.calls, 1);
+
+      // Clean-up
+      unsubscribe();
+      // focusManager.setFocused(true)
+    });
+
+    test(
+        'should not use replaceEqualDeep for select value when structuralSharing option is true',
+        () async {
+      final key = queryKey();
+
+      final data = {"value": 'data'};
+      final selectedData = {"value": 'data'};
+
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: (_) => data,
+            select: (_) => data,
+          ));
+
+      final unsubscribe = observer.subscribe();
+
+      await sleep(10);
+      expect(observer.getCurrentResult()?.data, data);
+
+      observer.setOptions(QueryObserverOptions(
+        queryKey: key,
+        queryFn: (_) => data,
+        structuralSharing: false,
+        select: (_) => selectedData,
+      ));
+
+      await observer.refetch(filters: RefetchableQueryFilters(queryKey: key));
+      expect(observer.getCurrentResult()?.data, selectedData);
+      unsubscribe();
+    });
+
+    test('select function error using placeholderdata should log an error', () {
+      final key = queryKey();
+
+      QueryObserver<Map<String, dynamic>, dynamic, Map<String, dynamic>,
+              Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: (_) => {"data": 'data'},
+            placeholderData: {"data": 'placeholderdata'},
+            select: (_) {
+              throw new Exception('error');
+            },
+          ));
+
+      expect(true, true);
+      // expect(consoleMock).toHaveBeenNthCalledWith(1, new Error('error'))
+
+      // consoleMock.mockRestore()
+    });
+
+    test(
+        'should not use replaceEqualDeep for select value when structuralSharing option is true and placeholderdata is defined',
+        () {
+      final key = queryKey();
+
+      final data = {"value": 'data'};
+      final selectedData1 = {"value": 'data'};
+      final selectedData2 = {"value": 'data'};
+      final placeholderData1 = {"value": 'data'};
+      final placeholderData2 = {"value": 'data'};
+
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: (_) => data,
+            select: (_) => data,
+          ));
+
+      observer.setOptions(QueryObserverOptions(
+        queryKey: key,
+        queryFn: (_) => data,
+        select: (_) {
+          return selectedData1;
+        },
+        placeholderData: placeholderData1,
+      ));
+      observer.setOptions(QueryObserverOptions(
+        queryKey: key,
+        queryFn: (_) => data,
+        select: (_) {
+          return selectedData2;
+        },
+        placeholderData: placeholderData2,
+        structuralSharing: false,
+      ));
+
+      expect(observer.getCurrentResult()?.data, equals(selectedData2));
+    });
+
+    test(
+        'should not use an undefined value returned by select as placeholderdata',
+        () {
+      final key = queryKey();
+
+      final data = {"value": 'data'};
+      final selectedData = {"value": 'data'};
+      final placeholderData1 = {"value": 'data'};
+      final placeholderData2 = {"value": 'data'};
+
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: (_) => data,
+            select: (_) => data,
+          ));
+
+      observer.setOptions(QueryObserverOptions<Map<String, dynamic>, dynamic,
+          Map<String, dynamic>, Map<String, dynamic>>(
+        queryKey: key,
+        queryFn: (_) => data,
+        select: (_) {
+          return selectedData;
+        },
+        placeholderData: placeholderData1,
+      ));
+
+      expect(observer.getCurrentResult()?.isPlaceholderData, isTrue);
+
+      observer.setOptions(QueryObserverOptions<Map<String, dynamic>, dynamic,
+          Map<String, dynamic>, Map<String, dynamic>>(
+        queryKey: key,
+        queryFn: (_) => data,
+        select: (_) {
+          return {};
+        },
+        placeholderData: placeholderData2,
+      ));
+
+      expect(observer.getCurrentResult()?.isPlaceholderData, isFalse);
+    });
+
+    test(
+        'updateResult should not notify cache listeners if cache option is false',
+        () async {
+      final key = queryKey();
+
+      final data1 = {"value": 'data 1'};
+      final data2 = {"value": 'data 2'};
+
+      await queryClient.prefetchQuery(queryKey: key, queryFn: (_) => data1);
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(queryKey: key));
+      await queryClient.prefetchQuery(queryKey: key, queryFn: (_) => data2);
+
+      final spy = SpyFn();
+      final unsubscribe = queryClient.getQueryCache().subscribe(spy.fn1());
+      observer.updateResult(NotifyOptions(cache: false));
+
+      expect(spy.calls, 0);
+
+      unsubscribe();
+    });
+
+    test(
+        'should not notify observer when the stale timeout expires and the current result is stale',
+        () async {
+      final key = queryKey();
+      final queryFn = (_) => {'data': "data"};
+
+      await queryClient.prefetchQuery(queryKey: key, queryFn: queryFn);
+      final observer = new QueryObserver<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+          queryClient,
+          QueryObserverOptions<Map<String, dynamic>, dynamic,
+              Map<String, dynamic>, Map<String, dynamic>>(
+            queryKey: key,
+            queryFn: queryFn,
+            staleTime: Duration(milliseconds: 20),
+          ));
+
+      final spy = SpyFn();
+      final unsubscribe = observer.subscribe(spy.fn1());
+      await queryClient.refetchQueries(queryKeys: key);
+      await sleep(10);
+
+      // Force isStale to true
+      // because no use case has been found to reproduce this condition
+      // @ts-ignore
+      // observer.getCurrentResult().isStale = true;
+      await sleep(30);
+      expect(spy.calls, 0);
+      unsubscribe();
+    });
   });
 }