add test for completed tasks view

Author: SimonLab

test/completed_tasks_test.dart

@@ -0,0 +1,29 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:todolist/models/task.dart';
+import 'package:todolist/models/todoList.dart';
+import 'package:todolist/screens/completed_tasks/completed_tasks.dart';
+
+void main() {
+  testWidgets('Test Todolist widget', (WidgetTester tester) async {
+    final todoList = TodoListModel();
+    final task = TaskModel(text: "task 1");
+    final task2 = TaskModel(text: "task 2");
+    final task3 = TaskModel(text: "task 3", completed: true);
+    todoList.addTaks(task);
+    todoList.addTaks(task2);
+    todoList.addTaks(task3);
+    await tester.pumpWidget(
+      MaterialApp(
+          home: CompletedTasks(todoList: todoList )
+          ),
+    );
+
+    final textTask1 = find.text('task 1');
+    final textTask2 = find.text('task 2');
+    final textTask3 = find.text('task 3');
+    expect(textTask1, findsNothing);
+    expect(textTask2, findsNothing);
+    expect(textTask3, findsOneWidget);
+  });
+}