diff --git a/test/service/todo_service_test.dart b/test/service/todo_service_test.dart
index 32459bd..edee3ba 100644
--- a/test/service/todo_service_test.dart
+++ b/test/service/todo_service_test.dart
@@ -36,21 +36,40 @@ void main() {
     todoService = container.read(todoServiceProvider);
   });
 
+  void initializeWhenCategory(String categoryId) {
+    final categoryCollectionRef = MockCollectionReference();
+    final categoryDocumentRef = MockDocumentReference();
+
+    when(
+      () => mockFirestoreInstance.collection(categoryCollection),
+    ).thenReturn(categoryCollectionRef);
+    when(
+      () => categoryCollectionRef.doc(categoryId),
+    ).thenAnswer((_) => categoryDocumentRef);
+    when(() => categoryDocumentRef.update(any())).thenAnswer(
+      (_) => Future.value(),
+    );
+  }
+
   group('$TodoService', () {
     test('Get $Todo list from Firebase mock', () async {
       // arrange
-      when(() => mockFirestoreInstance.collection(any()))
-          .thenReturn(mockCollectionReference);
+      const fieldName = 'categoryId';
+
+      when(
+        () => mockFirestoreInstance.collection(todoCollection),
+      ).thenReturn(mockCollectionReference);
 
       when(
         () => mockCollectionReference.where(
-          any(),
+          fieldName,
           isEqualTo: any(named: 'isEqualTo'),
         ),
       ).thenReturn(mockQuery);
 
-      when(() => mockQuery.snapshots())
-          .thenAnswer((_) => Stream.value(mockQuerySnapshot));
+      when(
+        () => mockQuery.snapshots(),
+      ).thenAnswer((_) => Stream.value(mockQuerySnapshot));
 
       when(() => mockQuerySnapshot.docs)
           .thenReturn([mockQueryDocumentSnapshot]);
@@ -66,26 +85,29 @@ void main() {
       expect(result, isA<Stream<List<Todo>>>());
       expect(finalResult, isA<List<Todo>>());
       expect(finalResult, [existingTodo]);
+
       verify(
         () => mockFirestoreInstance
-            .collection(any())
-            .where(any(), isEqualTo: any(named: 'isEqualTo')),
+            .collection(todoCollection)
+            .where(fieldName, isEqualTo: any(named: 'isEqualTo')),
       ).called(1);
     });
 
     test('Get $Todo by id from Firebase mock', () async {
       // arrange
-      when(() => mockFirestoreInstance.collection(any()))
-          .thenReturn(mockCollectionReference);
+      when(
+        () => mockFirestoreInstance.collection(todoCollection),
+      ).thenReturn(mockCollectionReference);
 
-      when(() => mockCollectionReference.doc(any()))
-          .thenReturn(mockDocumentReference);
+      when(
+        () => mockCollectionReference.doc(todoId),
+      ).thenReturn(mockDocumentReference);
 
-      when(() => mockDocumentReference.get())
-          .thenAnswer((_) => Future.value(mockDocumentSnapshot));
+      when(
+        () => mockDocumentReference.get(),
+      ).thenAnswer((_) => Future.value(mockDocumentSnapshot));
 
       when(() => mockDocumentSnapshot.exists).thenReturn(true);
-
       when(() => mockDocumentSnapshot.toMap).thenReturn(existingTodo.toJson());
 
       // act
@@ -96,23 +118,27 @@ void main() {
       expect(result, isA<Future<Todo>>());
       expect(finalResult, isA<Todo>());
       expect(finalResult, existingTodo);
-      verify(() => mockFirestoreInstance.collection(any()).doc(any()))
-          .called(1);
+
+      verify(
+        () => mockFirestoreInstance.collection(todoCollection).doc(todoId),
+      ).called(1);
     });
 
     test("Get $Exception if todo by id doesn't exists", () async {
       // arrange
-      when(() => mockFirestoreInstance.collection(any()))
-          .thenReturn(mockCollectionReference);
+      when(
+        () => mockFirestoreInstance.collection(todoCollection),
+      ).thenReturn(mockCollectionReference);
 
-      when(() => mockCollectionReference.doc(any()))
-          .thenReturn(mockDocumentReference);
+      when(
+        () => mockCollectionReference.doc(todoId),
+      ).thenReturn(mockDocumentReference);
 
-      when(() => mockDocumentReference.get())
-          .thenAnswer((_) => Future.value(mockDocumentSnapshot));
+      when(
+        () => mockDocumentReference.get(),
+      ).thenAnswer((_) => Future.value(mockDocumentSnapshot));
 
       when(() => mockDocumentSnapshot.exists).thenReturn(false);
-
       when(() => mockDocumentSnapshot.toMap).thenThrow(
         Exception('Oops!!! Todo not found'),
       );
@@ -121,76 +147,95 @@ void main() {
       final result = todoService.getTodoById(categoryId, existingTodo.id!);
 
       // assert
-      expect(result, throwsA(isA<Exception>()));
-      verify(() => mockFirestoreInstance.collection(any()).doc(any()))
-          .called(1);
+      await expectLater(result, throwsA(isA<Exception>()));
+
+      verify(
+        () => mockFirestoreInstance.collection(todoCollection).doc(todoId),
+      ).called(1);
     });
 
     test('Save $Todo from Firebase mock', () {
       // arrange
-      when(() => mockFirestoreInstance.collection(any()))
-          .thenReturn(mockCollectionReference);
-
-      when(() => mockCollectionReference.add(any()))
-          .thenAnswer((_) async => mockDocumentReference);
+      initializeWhenCategory(initialTodo.categoryId);
 
-      when(() => mockCollectionReference.doc(any()))
-          .thenReturn(mockDocumentReference);
-
-      when(() => mockDocumentReference.update(any()))
-          .thenAnswer((_) => Future.value());
+      when(
+        () => mockFirestoreInstance.collection(todoCollection),
+      ).thenReturn(mockCollectionReference);
+      when(
+        () => mockCollectionReference.add(initialTodo.toJson()),
+      ).thenAnswer((_) async => mockDocumentReference);
 
       // act
       final result = todoService.saveTodo(initialTodo);
 
       // assert
       expect(result, isA<Future<void>>());
-      verify(() => mockFirestoreInstance.collection(any()).add(any()))
-          .called(1);
+
+      verify(
+        () => mockFirestoreInstance
+            .collection(todoCollection)
+            .add(initialTodo.toJson()),
+      ).called(1);
     });
 
     test('Update $Todo from Firebase mock', () {
       // arrange
-      when(() => mockFirestoreInstance.collection(any()))
-          .thenReturn(mockCollectionReference);
+      final path = existingTodo.id!;
+      final data = existingTodo.toJson();
 
-      when(() => mockCollectionReference.doc(any()))
-          .thenReturn(mockDocumentReference);
+      when(
+        () => mockFirestoreInstance.collection(todoCollection),
+      ).thenReturn(mockCollectionReference);
 
-      when(() => mockDocumentReference.update(any()))
-          .thenAnswer((_) => Future.value());
+      when(
+        () => mockCollectionReference.doc(path),
+      ).thenReturn(mockDocumentReference);
+
+      when(
+        () => mockDocumentReference.update(data),
+      ).thenAnswer((_) => Future.value());
 
       // act
       final result = todoService.saveTodo(existingTodo.copyWith());
 
       // assert
       expect(result, isA<Future<void>>());
+
       verify(
-        () => mockFirestoreInstance.collection(any()).doc(any()).update(any()),
-      );
+        () => mockFirestoreInstance
+            .collection(todoCollection)
+            .doc(path)
+            .update(data),
+      ).called(1);
     });
 
     test('Remove $Todo from Firebase mock', () {
       // arrange
-      when(() => mockFirestoreInstance.collection(any()))
-          .thenReturn(mockCollectionReference);
-
-      when(() => mockCollectionReference.doc(any()))
-          .thenReturn(mockDocumentReference);
+      initializeWhenCategory(existingTodo.categoryId);
 
-      when(() => mockDocumentReference.delete())
-          .thenAnswer((_) => Future.value());
-
-      when(() => mockDocumentReference.update(any()))
-          .thenAnswer((_) => Future.value());
+      when(
+        () => mockFirestoreInstance.collection(todoCollection),
+      ).thenReturn(mockCollectionReference);
+      when(
+        () => mockCollectionReference.doc(existingTodo.id),
+      ).thenReturn(mockDocumentReference);
+      when(mockDocumentReference.delete).thenAnswer((_) => Future.value());
 
       // act
-      final result = todoService.deleteTodo(existingTodo.id!, category.id!);
+      final result = todoService.deleteTodo(
+        existingTodo.id!,
+        existingTodo.categoryId,
+      );
 
       // assert
       expect(result, isA<Future<void>>());
-      verify(() => mockFirestoreInstance.collection(any()).doc(any()).delete())
-          .called(1);
+
+      verify(
+        () => mockFirestoreInstance
+            .collection(todoCollection)
+            .doc(existingTodo.id)
+            .delete(),
+      ).called(1);
     });
   });
 }