Refactor the City and its tests.

tests/Feature/Validation/CityValidationTest.php

@@ -0,0 +1,37 @@
+<?php
+
+namespace Tests\Feature;
+
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Illuminate\Foundation\Testing\WithFaker;
+use Tests\TestCase;
+
+use App\Models\City;
+
+class CityValidationTest extends TestCase
+{
+    public function testCityWithEmptyName(): void
+    {
+        $json = City::validateWithName('');
+
+        $this->assertEquals($json['error'], 'The city name is empty, please, write the name!!!');
+    }
+
+    public function testNotExistingCityWithName(): void
+    {
+        $name = '404 City';
+
+        $json = City::validateWithName($name);
+
+        $this->assertEquals($json['error'], 'A city with the name does not exist!!!');
+    }
+
+    public function testValidCityWithName(): void
+    {
+        $name = 'testCity';
+
+        $json = City::validateWithName($name);
+
+        $this->assertEquals($json['ok'], 'A city with the name is valid.');
+    }
+}