add empty string tests for authenticate

backend/tests/Unit/Auth/UseCases/AuthenticateUserTest.php

@@ -58,6 +58,24 @@ class AuthenticateUserTest extends TestCase
         $this->authenticateUser->execute($request);
     }
 
+    public function testThrowsWhenEmailEmpty(): void
+    {
+        $this->expectException(BadRequestException::class);
+        $this->expectExceptionMessage('email is required');
+
+        $request = new AuthenticateUserRequest('', 'secret');
+        $this->authenticateUser->execute($request);
+    }
+
+    public function testThrowsWhenPasswordEmpty(): void
+    {
+        $this->expectException(BadRequestException::class);
+        $this->expectExceptionMessage('password is required');
+
+        $request = new AuthenticateUserRequest('user@example.com', '');
+        $this->authenticateUser->execute($request);
+    }
+
     public function testThrowsWhenUserNotFound(): void
     {
         $this->expectException(UnauthorizedException::class);