Make &stringify_keys/1 private.

Since &keys_to_string/1 is public, also add a test case to coverage for
&stringify_keys/1.

Drop useless `stringify_keys(nil)` case.
Continue intercepting %DateTime{} before it matches %{}

Author: arubis

lib/code_corps/map_utils.ex

@@ -7,18 +7,18 @@ defmodule CodeCorps.MapUtils do
 
   def keys_to_string(map), do: stringify_keys(map)
 
+  # Intercept incoming %DateTime arguments; otherwise they will match %{}
+  defp stringify_keys(%DateTime{} = val), do: val
   # Goes through a list and stringifies keys of any map member
-  def stringify_keys(nil), do: nil
-  def stringify_keys(map = %{}) do
+  defp stringify_keys(map = %{}) do
     map
     |> Enum.map(fn {k, v} -> {stringify_key(k), stringify_keys(v)} end)
     |> Enum.into(%{})
   end
-  def stringify_keys([head | rest]), do: [stringify_keys(head) | stringify_keys(rest)]
+  defp stringify_keys([head | rest]), do: [stringify_keys(head) | stringify_keys(rest)]
   # Default
-  def stringify_keys(not_a_map), do: not_a_map
-
-  def stringify_key(k) when is_atom(k), do: Atom.to_string(k)
-  def stringify_key(k), do: k
+  defp stringify_keys(val), do: val
 
+  defp stringify_key(k) when is_atom(k), do: Atom.to_string(k)
+  defp stringify_key(k), do: k
 end

test/lib/code_corps/map_utils_test.exs

@@ -1,9 +1,14 @@
 defmodule CodeCorps.MapUtilsTest do
   use ExUnit.Case, async: true
 
-  import CodeCorps.MapUtils, only: [rename: 3]
+  import CodeCorps.MapUtils, only: [keys_to_string: 1, rename: 3]
 
   test "&rename/3 renames old key in map to new key" do
     assert %{"foo" => 2} |> rename("foo", "bar") == %{"bar" => 2}
   end
+
+  test "&keys_to_string/1 stringifies any keys in map" do
+    assert %{:a => "one", :b => "two"} |> keys_to_string == %{"a" => "one", "b" => "two"}
+    assert %{} |> keys_to_string == %{}
+  end
 end