Add unit model test

tests/Unit/Integration/UnitTest.php

@@ -0,0 +1,24 @@
+<?php
+
+namespace Tests\Unit\Integration;
+
+use App\Unit;
+use App\Product;
+use Tests\TestCase;
+use Illuminate\Database\Eloquent\Collection;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+
+class UnitTest extends TestCase
+{
+    use RefreshDatabase;
+
+    /** @test */
+    public function a_unit_has_many_products_relation()
+    {
+        $unit = factory(Unit::class)->create();
+        $product = factory(Product::class)->create(['unit_id' => $unit->id]);
+
+        $this->assertInstanceOf(Collection::class, $unit->products);
+        $this->assertInstanceOf(Product::class, $unit->products->first());
+    }
+}