Added missing login page (#339)

provider_shopper/lib/main.dart

@@ -9,6 +9,7 @@ import 'package:provider_shopper/models/cart.dart';
 import 'package:provider_shopper/models/catalog.dart';
 import 'package:provider_shopper/screens/cart.dart';
 import 'package:provider_shopper/screens/catalog.dart';
+import 'package:provider_shopper/screens/login.dart';
 
 void main() {
   runApp(MyApp());
@@ -39,7 +40,8 @@ class MyApp extends StatelessWidget {
         theme: appTheme,
         initialRoute: '/',
         routes: {
-          '/': (context) => MyCatalog(),
+          '/': (context) => MyLogin(),
+          '/catalog': (context) => MyCatalog(),
           '/cart': (context) => MyCart(),
         },
       ),

provider_shopper/lib/screens/login.dart

@@ -0,0 +1,48 @@
+// Copyright 2020 The Flutter team. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+class MyLogin extends StatelessWidget {
+  @override
+  Widget build(BuildContext context) {
+    return Scaffold(
+      body: Center(
+        child: Container(
+          padding: EdgeInsets.all(80.0),
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: [
+              Text(
+                'Welcome',
+                style: Theme.of(context).textTheme.display4,
+              ),
+              TextFormField(
+                decoration: InputDecoration(
+                  hintText: 'Username',
+                ),
+              ),
+              TextFormField(
+                decoration: InputDecoration(
+                  hintText: 'Password',
+                ),
+                obscureText: true,
+              ),
+              SizedBox(
+                height: 24,
+              ),
+              RaisedButton(
+                color: Colors.yellow,
+                child: Text('ENTER'),
+                onPressed: () {
+                  Navigator.pushReplacementNamed(context, '/catalog');
+                },
+              )
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}

provider_shopper/test/widget_test.dart

@@ -11,6 +11,10 @@ void main() {
     // Build our app and trigger a frame.
     await tester.pumpWidget(MyApp());
 
+    // Navigating through login page.
+    await tester.tap(find.text('ENTER'));
+    await tester.pumpAndSettle();
+
     // Check that shopping cart is empty at start.
     await tester.tap(find.byIcon(Icons.shopping_cart));
     await tester.pumpAndSettle();