Add a normalization step to protect code from irregularities

test/hillel_budget_test.exs

@@ -18,6 +18,46 @@ defmodule HillelBudgetTest do
     %{total_limit: total_limit}
   end
 
+  # After beginning to work on categories, I decided I didn't want to
+  # have to keep hassling with counts, so add a "normalization" step
+  # to clean the data.
+  #
+  # Besides, I'm guessing this will make things easier later on.
+
+  def normalize(bill) when is_map(bill) do
+    cost = bill.cost
+    categories = Map.get(bill, :categories, [])
+    count = Map.get(bill, :count, 1)
+
+    Enum.map(1..count, fn _ ->
+      %{cost: cost, categories: categories}
+    end)
+  end
+
+  def normalize(bills) when is_list(bills) do
+    Enum.flat_map(bills, &normalize/1)
+  end
+
+  describe "normalization" do
+    test "normalizing a bill" do
+      expect = fn bill, expected ->
+        assert normalize(bill) == expected
+      end
+
+      %{cost: "c"}                    |> expect.([%{cost: "c", categories: []}])
+      %{cost: "c", categories: ["a"]} |> expect.([%{cost: "c", categories: ["a"]}])
+      %{cost: "c", categories: ["a", "b"], count: 2}
+                                      |> expect.([%{cost: "c", categories: ["a", "b"]},
+                                                  %{cost: "c", categories: ["a", "b"]}])
+    end
+
+    test "normalizing bills" do
+      actual = normalize([%{cost: 20, count: 2}])
+      assert actual == [%{cost: 20, categories: []},
+                        %{cost: 20, categories: []}]
+    end
+  end
+
   describe "total budget" do 
     test "total budget boundaries" do
       bill = [%{cost: 50}]
@@ -32,4 +72,10 @@ defmodule HillelBudgetTest do
       refute can_afford?(budget(59), bill)
     end
   end
+
+  describe "interaction of limits" do
+    @tag :skip
+    test "category with total"
+  end
+
 end