Return {:error, :already_mocked} when using new/1,2 over mock (#25)

lib/nuntiux.ex

@@ -89,9 +89,15 @@ defmodule Nuntiux do
         when process_name: process_name(),
              opts: opts(),
              ok: :ok,
-             error: {:error, :not_found}
+             error: {:error, :not_found | :already_mocked}
   def new(process_name, opts \\ %{}) do
-    Nuntiux.Supervisor.start_mock(process_name, opts)
+    case mocked_process(process_name) do
+      {:error, :not_mocked} ->
+        Nuntiux.Supervisor.start_mock(process_name, opts)
+
+      _pid ->
+        {:error, :already_mocked}
+    end
   end
 
   @doc """
@@ -105,6 +111,9 @@ defmodule Nuntiux do
       {:error, :not_found} ->
         raise(Nuntiux.Exception, message: "Process #{process_name} not found.")
 
+      {:error, :already_mocked} ->
+        raise(Nuntiux.Exception, message: "Process #{process_name} is already mocked.")
+
       :ok ->
         process_name
     end

test/nuntiux_test.exs

@@ -476,6 +476,15 @@ defmodule NuntiuxTest do
       assert captured_log =~ "expect_id: :no_head_matches"
       assert captured_log =~ ":function_clause"
     end
+
+    test "new!/1 raises an exception if trying to mock a mock", %{
+      plus_oner_name: plus_oner_name
+    } do
+      assert_raise(Nuntiux.Exception, ~r/^Process .* is already mocked\.$/, fn ->
+        Nuntiux.new!(plus_oner_name)
+        Nuntiux.new!(plus_oner_name)
+      end)
+    end
   end
 
   defp send2(dest, msg) do