plan repo with create method

tests/Fakes/FakePlanRepository.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace Tests\Fakes;
+
+use App\Plan\CreatePlanDto;
+use App\Plan\Plan;
+use App\Plan\PlanRepository;
+
+class FakePlanRepository implements PlanRepository
+{
+    private array $existingPlans = [];
+
+    public function create(CreatePlanDto $dto): Plan
+    {
+        $id = $this->nextId();
+        $plan = new Plan(
+            id: $id,
+            name: $dto->name,
+        );
+        $this->existingPlans[$id] = $plan;
+
+        return $plan;
+    }
+
+    private function nextId(): int
+    {
+        return count($this->existingPlans);
+    }
+}