add tests

test/support/parser_halt_format.ex

@@ -0,0 +1,24 @@
+defmodule FeedReader.TestSupport.ParserHaltFormat do
+  @behaviour FeedReader.Format
+
+  @impl true
+  def id, do: :parser_halt
+
+  @impl true
+  def matches_prefix?(_prefix), do: true
+
+  @impl true
+  def handler, do: FeedReader.TestSupport.ParserHaltHandler
+
+  @impl true
+  def new_parser_state(_event_sink, opts) do
+    if Keyword.get(opts, :normal_exit), do: exit(:normal)
+    nil
+  end
+
+  @impl true
+  def normalize_feed(_state, _opts), do: %FeedReader.Feed{}
+
+  @impl true
+  def normalize_item(_raw_item, _feed, _opts), do: :skip
+end