feat: add product sorting to collection pages with tests

Add sort functionality to /collections/:slug pages with 6 sort options
(featured, newest, price ascending/descending, name A-Z/Z-A). Sort
selection persists across category navigation via URL query params.

Refactor handle_params to be DRY using load_collection/1 helper.
Add comprehensive unit tests for PreviewData category functions and
LiveView tests for the Collection page sorting and navigation.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

test/simpleshop_theme_web/live/shop_live/collection_test.exs

@@ -0,0 +1,154 @@
+defmodule SimpleshopThemeWeb.ShopLive.CollectionTest do
+  use SimpleshopThemeWeb.ConnCase, async: false
+
+  import Phoenix.LiveViewTest
+
+  alias SimpleshopTheme.Theme.PreviewData
+
+  describe "Collection page" do
+    test "renders collection page for /collections/all", %{conn: conn} do
+      {:ok, _view, html} = live(conn, ~p"/collections/all")
+
+      assert html =~ "All Products"
+    end
+
+    test "renders collection page for specific category", %{conn: conn} do
+      category = List.first(PreviewData.categories())
+      {:ok, _view, html} = live(conn, ~p"/collections/#{category.slug}")
+
+      assert html =~ category.name
+    end
+
+    test "displays products", %{conn: conn} do
+      {:ok, _view, html} = live(conn, ~p"/collections/all")
+
+      products = PreviewData.products()
+      first_product = List.first(products)
+
+      assert html =~ first_product.name
+    end
+
+    test "displays category filter buttons", %{conn: conn} do
+      {:ok, _view, html} = live(conn, ~p"/collections/all")
+
+      categories = PreviewData.categories()
+
+      for category <- categories do
+        assert html =~ category.name
+      end
+    end
+
+    test "displays sort dropdown", %{conn: conn} do
+      {:ok, _view, html} = live(conn, ~p"/collections/all")
+
+      assert html =~ "Featured"
+      assert html =~ "Newest"
+      assert html =~ "Price: Low to High"
+      assert html =~ "Price: High to Low"
+      assert html =~ "Name: A-Z"
+      assert html =~ "Name: Z-A"
+    end
+
+    test "redirects to /collections/all for unknown category", %{conn: conn} do
+      {:error, {:live_redirect, %{to: to, flash: flash}}} =
+        live(conn, ~p"/collections/nonexistent")
+
+      assert to == "/collections/all"
+      assert flash["error"] == "Collection not found"
+    end
+
+    test "filters products by category", %{conn: conn} do
+      category = List.first(PreviewData.categories())
+      {:ok, _view, html} = live(conn, ~p"/collections/#{category.slug}")
+
+      products = PreviewData.products_by_category(category.slug)
+
+      for product <- products do
+        assert html =~ product.name
+      end
+    end
+  end
+
+  describe "Sorting" do
+    test "sorts by price ascending", %{conn: conn} do
+      {:ok, view, _html} = live(conn, ~p"/collections/all")
+
+      html =
+        view
+        |> element("form[phx-change='sort_changed']")
+        |> render_change(%{sort: "price_asc"})
+
+      assert html =~ "Price: Low to High"
+    end
+
+    test "sorts by price descending", %{conn: conn} do
+      {:ok, view, _html} = live(conn, ~p"/collections/all")
+
+      html =
+        view
+        |> element("form[phx-change='sort_changed']")
+        |> render_change(%{sort: "price_desc"})
+
+      assert html =~ "Price: High to Low"
+    end
+
+    test "sorts by name ascending", %{conn: conn} do
+      {:ok, view, _html} = live(conn, ~p"/collections/all")
+
+      html =
+        view
+        |> element("form[phx-change='sort_changed']")
+        |> render_change(%{sort: "name_asc"})
+
+      assert html =~ "Name: A-Z"
+    end
+
+    test "sorts by name descending", %{conn: conn} do
+      {:ok, view, _html} = live(conn, ~p"/collections/all")
+
+      html =
+        view
+        |> element("form[phx-change='sort_changed']")
+        |> render_change(%{sort: "name_desc"})
+
+      assert html =~ "Name: Z-A"
+    end
+
+    test "sort parameter is preserved in URL", %{conn: conn} do
+      {:ok, view, _html} = live(conn, ~p"/collections/all?sort=price_asc")
+
+      html = render(view)
+
+      assert html =~ "selected"
+    end
+
+    test "default sort is featured", %{conn: conn} do
+      {:ok, _view, html} = live(conn, ~p"/collections/all")
+
+      assert html =~ ~r/<option[^>]*value="featured"[^>]*selected/
+    end
+  end
+
+  describe "Navigation" do
+    test "category links preserve sort order", %{conn: conn} do
+      {:ok, _view, html} = live(conn, ~p"/collections/all?sort=price_desc")
+
+      category = List.first(PreviewData.categories())
+      assert html =~ "/collections/#{category.slug}?sort=price_desc"
+    end
+
+    test "All button link preserves sort order", %{conn: conn} do
+      {:ok, _view, html} = live(conn, ~p"/collections/art-prints?sort=name_asc")
+
+      assert html =~ "/collections/all?sort=name_asc"
+    end
+
+    test "featured sort does not include query param in links", %{conn: conn} do
+      {:ok, _view, html} = live(conn, ~p"/collections/all")
+
+      category = List.first(PreviewData.categories())
+      assert html =~ ~s(href="/collections/#{category.slug}")
+      refute html =~ "/collections/#{category.slug}?sort=featured"
+    end
+  end
+end