diff --git a/app/Models/User.php b/app/Models/User.php
index 6a41429..4f83a9c 100644
--- a/app/Models/User.php
+++ b/app/Models/User.php
@@ -41,5 +41,6 @@ class User extends Authenticatable
      */
     protected $casts = [
         'email_verified_at' => 'datetime',
+        'is_admin' => 'boolean',
     ];
 }
diff --git a/tests/Feature/ValidationTest.php b/tests/Feature/ValidationTest.php
index afc187e..eac1799 100644
--- a/tests/Feature/ValidationTest.php
+++ b/tests/Feature/ValidationTest.php
@@ -94,7 +94,7 @@ class ValidationTest extends TestCase
 
         $user = User::where('name', $updatedUser['name'])->first();
         $this->assertNotNull($user);
-        $this->assertEquals(false, $user->is_admin);
+        $this->assertFalse($user->is_admin);
     }
 
     public function test_custom_error_message()
@@ -107,6 +107,8 @@ class ValidationTest extends TestCase
     public function test_custom_validation_rule()
     {
         $response = $this->post('articles', ['title' => 'lowercase']);
-        $response->assertSessionHasErrors('title')->assertStatus(302);
+        $response->assertSessionHasErrors([
+            'title' => 'The title does not start with an uppercased letter.',
+        ])->assertStatus(302);
     }
 }