Code for step 3

lib/store_inventory/test_repo.ex

@@ -0,0 +1,37 @@
+defmodule StoreInventory.TestRepo do
+  alias Ecto.Changeset
+  alias StoreInventory.Item
+
+  def all(Item, _opts \\ []) do
+    [
+      %Item{
+        name: "Thing 1",
+        description: "A really cool thing",
+        price: 100,
+        quantity: 2
+      },
+      %Item{
+        name: "Thing 2",
+        description: "Another really cool thing",
+        price: 50,
+        quantity: 0
+      },
+      %Item{
+        name: "Thing 3",
+        description: "A really cool thing",
+        price: 75,
+        quantity: 5
+      }
+    ]
+  end
+
+  def insert(changeset, opts \\ [])
+
+  def insert(%Changeset{errors: [], changes: values}, _opts) do
+    {:ok, struct(Item, values)}
+  end
+
+  def insert(changeset, _opts) do
+    {:error, changeset}
+  end
+end

test/store_inventory_test.exs

@@ -1,8 +1,35 @@
 defmodule StoreInventoryTest do
   use ExUnit.Case
-  doctest StoreInventory
 
-  test "greets the world" do
-    assert StoreInventory.hello() == :world
+  alias Ecto.Changeset
+  alias StoreInventory.Item
+
+  test "insert_item/1 should return an error when invalid params are provided" do
+    params = %{
+      name: "Item",
+      description: "Something people want",
+      price: 1,
+      quantity: "INVALID"
+    }
+
+    {:error, changeset} = StoreInventory.insert_item(params)
+
+    expected_error = {"is invalid", [type: :integer, validation: :cast]}
+    assert %Changeset{errors: [quantity: ^expected_error]} = changeset
+  end
+
+  test "insert_item/1 should return an :ok tuple when valid params are provided" do
+    params = %{
+      name: "Item",
+      description: "Something people want",
+      price: 1,
+      quantity: 5
+    }
+
+    assert {:ok, %Item{}} = StoreInventory.insert_item(params)
+  end
+
+  test "average_item_price/0 should return the average price of all the items in the DB" do
+    assert 75.0 = StoreInventory.average_item_price()
   end
 end