Failed asserting that two strings are equal.

I have a test that can test if an admin can edit products

and when I run it I get the error Failed asserting that two strings are equal. how can I fix this?

Test

public function test_admin_can_edit_products()
    {
        $this->withExceptionHandling();

        $user = User::factory()->create(['admin' => 1]);

        $product = Product::factory()->create();

        $response = $this->actingAs($user)->patch('/admin/product/' . $product->slug, [
            'name' => 'iPhone X',
            'description' => 'This is a new iphone',
            'price' => 220,
        ]);

        $response->assertRedirect(route('product.index'));
    }

my edit controller

public function update(Request $request, Product $product)
    {
        $validated  = $request->validate([
            'name' => 'required|unique:products,name,' . $product->id,
            'slug' => 'required|unique:products,slug,' . $product->id,
            'price' => 'required|integer',
            'description' => 'required',
        ]);


        $product->update($validated);

        $this->calculateDiscount($product);

        return redirect(route('product.index'));
    }

private function calculateDiscount(Product $product)
    {
        if($product->price >= 112 && $product->price <= 115) {
            $percentage = 0.25;
            $price = $product->price;

            $discount = ($percentage / 100) * $price;

            if($product->discount()->exists()){
                $product->discount()->update(['discount' => $discount]);

            } else {

                $product->discount()->create(['discount' => $discount]);
            }
        }

        if($product->price >= 120) {
            $percentage = 0.50;
            $price = $product->price;

            $discount = ($percentage / 100) * $price;

            $product->discount()->create(['discount' => $discount]);
        }
    }