add tests

test/feed_reader/format_detection_test.exs

@@ -0,0 +1,43 @@
+defmodule FeedReader.FormatDetectionTest do
+  use ExUnit.Case, async: true
+
+  alias FeedReader.TestSupport.ExternalFormat
+
+  test "detects RSS, Atom, and RDF from a bounded XML prefix" do
+    assert FeedReader.detect_format("<?xml version='1.0'?><rss version='2.0'>") == :rss
+    assert FeedReader.detect_format("<feed xmlns='http://www.w3.org/2005/Atom'>") == :atom
+    assert FeedReader.detect_format("<rdf:RDF xmlns:rdf='urn:rdf'>") == :rdf
+    assert FeedReader.detect_format("<html><body>not a feed</body></html>") == :unknown
+  end
+
+  test "custom format detection replays the bounded prefix and unread chunks" do
+    chunks = ["<external-feed>tail", "continued"]
+
+    {format, _prefix, replay} =
+      FeedReader.FormatDetector.detect_and_replay(chunks,
+        formats: [ExternalFormat],
+        max_detection_bytes: 15
+      )
+
+    assert format == :external_test
+    assert replay |> Enum.to_list() |> IO.iodata_to_binary() == IO.iodata_to_binary(chunks)
+    assert FeedReader.detect_format("<feed><rss version='2.0'>") == :rss
+  end
+
+  test "detection does not inspect content beyond the configured prefix" do
+    content = String.duplicate("x", 12) <> "<rss version='2.0'>"
+
+    assert FeedReader.detect_format(content, max_detection_bytes: 12) == :unknown
+    assert FeedReader.detect_format(content, max_detection_bytes: 40) == :rss
+  end
+
+  test "validation checks only the explicitly selected format" do
+    rss = "<rss version='2.0'><channel></channel></rss>"
+
+    assert FeedReader.validate(rss, :rss)
+    assert FeedReader.validate(rss, FeedReader.Formats.RSS)
+    refute FeedReader.validate(rss, :atom)
+    refute FeedReader.validate(rss, :unknown)
+    assert FeedReader.validate("<external-feed>", ExternalFormat)
+  end
+end