[HAR-576] Create Item schema with changeset validation

test/items_api/item_test.exs

@@ -0,0 +1,96 @@
+defmodule ItemsApi.ItemTest do
+  use ExUnit.Case, async: true
+
+  alias ItemsApi.Item
+
+  describe "changeset/2" do
+    test "returns invalid changeset when no attrs provided" do
+      changeset = Item.changeset(%Item{}, %{})
+
+      refute changeset.valid?
+    end
+
+    test "returns valid changeset with name" do
+      changeset = Item.changeset(%Item{}, %{"name" => "test"})
+
+      assert changeset.valid?
+    end
+
+    test "changeset error for missing name includes correct message" do
+      changeset = Item.changeset(%Item{}, %{})
+
+      errors = errors_on(changeset)
+      assert errors == %{"name" => ["name is required"]}
+    end
+
+    test "returns valid changeset with name and description" do
+      changeset = Item.changeset(%Item{}, %{"name" => "Widget", "description" => "A fine widget"})
+
+      assert changeset.valid?
+      assert Ecto.Changeset.get_change(changeset, :name) == "Widget"
+      assert Ecto.Changeset.get_change(changeset, :description) == "A fine widget"
+    end
+
+    test "description defaults to empty string" do
+      changeset = Item.changeset(%Item{}, %{"name" => "test"})
+
+      assert changeset.valid?
+      # description is not in the changeset changes because the default is on the schema
+      assert Ecto.Changeset.get_field(changeset, :description) == ""
+    end
+
+    test "rejects empty string name" do
+      changeset = Item.changeset(%Item{}, %{"name" => ""})
+
+      refute changeset.valid?
+      errors = errors_on(changeset)
+      assert Map.has_key?(errors, "name")
+    end
+  end
+
+  describe "schema" do
+    test "has correct fields" do
+      fields = Item.__schema__(:fields)
+
+      assert :id in fields
+      assert :name in fields
+      assert :description in fields
+      assert :inserted_at in fields
+      refute :updated_at in fields
+    end
+
+    test "field types are correct" do
+      assert Item.__schema__(:type, :id) == :id
+      assert Item.__schema__(:type, :name) == :string
+      assert Item.__schema__(:type, :description) == :string
+      assert Item.__schema__(:type, :inserted_at) == :utc_datetime
+    end
+  end
+
+  describe "JSON encoding" do
+    test "encodes only specified fields" do
+      item = %Item{
+        id: 1,
+        name: "Test",
+        description: "Desc",
+        inserted_at: ~U[2026-01-01 00:00:00Z]
+      }
+
+      json = Jason.encode!(item)
+      decoded = Jason.decode!(json)
+
+      assert Map.has_key?(decoded, "id")
+      assert Map.has_key?(decoded, "name")
+      assert Map.has_key?(decoded, "description")
+      assert Map.has_key?(decoded, "inserted_at")
+      assert map_size(decoded) == 4
+    end
+  end
+
+  # Helper to extract errors from a changeset into a simpler map format
+  defp errors_on(changeset) do
+    Ecto.Changeset.traverse_errors(changeset, fn {msg, _opts} -> msg end)
+    |> Enum.map(fn {key, messages} -> {to_string(key), messages} end)
+    |> Map.new()
+  end
+end