Added missing tests for the firestore provider

lib/src/models/event_model.dart

@@ -86,7 +86,6 @@ class EventModel {
       mediumPriority.hashCode ^
       lowPriority.hashCode;
 
-  //  TODO: find a way to compare the 3 commented properties.
   @override
   bool operator ==(Object other) =>
       identical(this, other) ||

lib/src/models/task_model.dart

@@ -111,19 +111,6 @@ class TaskModel {
     }
   }
 
-  /// Returns a sample [TaskModel] with mock data.
-  static TaskModel sample() {
-    return TaskModel(
-      id: '1',
-      text:
-          'Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut.',
-      done: false,
-      ownerUsername: 'testUser',
-      event: 'testEvent',
-      priority: TaskPriority.medium,
-    );
-  }
-
   @override
   int get hashCode =>
       id.hashCode ^

lib/src/resources/firestore_provider.dart

@@ -42,8 +42,6 @@ class FirestoreProvider {
     return Observable(mappedStream);
   }
 
-  //TODO: add tests for this method.
-
   /// Returns a [UserModel].
   /// Only one out of id or username can be provided, if both are provided id
   /// will have higher priority.
@@ -251,8 +249,6 @@ class FirestoreProvider {
     return Observable(mappedStream);
   }
 
-  //TODO: add tests for this method.
-
   /// Returns an [EventModel].
   /// Only one out of id or name can be provided, if both are provided id
   /// will have higher priority.