Add UserValidatorByMatrixUserName.

app/Models/Validation/Validators/UserValidatorByMatrixUserName.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace App\Models\Validation\Validators;
+
+use App\Models\Validation\Validators\NextValidatorByName;
+use App\Models\User;
+
+class UserValidatorByMatrixUserName extends NextValidatorByName
+{
+    public function isCurrentValid(): bool
+    {
+        $count = User::where('matrix_username', $this->getName())->count();
+
+        return $count != 0;
+    }
+}
+

tests/Feature/Validation/Validators/UserValidatorByMatrixUserNameTest.php

@@ -0,0 +1,44 @@
+<?php
+
+namespace Tests\Feature;
+
+use Tests\TestCase;
+
+use App\Models\Validation\Validators\UserValidatorByMatrixUserName;
+use App\Models\Validation\Validators\OkValidator;
+
+class UserValidatorByMatrixUserNameTest extends TestCase
+{
+    public function dataProvider() {
+        return [
+            'Found Case' => [
+                'name' => '@test:test.com',
+                'isValid' => true,
+            ],
+            'Not Found Case' => [
+                'name' => '@kostia:test.com',
+                'isValid' => false,
+            ],
+            'Invalid Case' => [
+                'name' => '',
+                'isValid' => false,
+            ],
+        ];
+    }
+
+    public function setUpValidator(string $name): UserValidatorByMatrixUserName
+    {
+        return new UserValidatorByMatrixUserName($name, new OkValidator());
+    }
+
+    /**
+     * @dataProvider dataProvider
+     */
+    public function testGetMessage(string $name, bool $isValid): void
+    {
+        $validator = $this->setUpValidator($name);
+
+        $this->assertEquals($validator->isValid(), $isValid);
+    }
+}
+