ML-193: add secondary parser, search, and API coverage tests

Add ~80 focused tests across 10 files covering:

- Record set search by name, description, contained record title, artist name
- Navigation events for records, artists, record sets, links, and view-all actions
- MusicBrainz.ReleaseGroup parser (artist credits, included RGs, release IDs, types)
- MusicBrainz.ReleaseSearchResult edge cases (missing RG, unknown formats)
- LastFm.Session XML edge cases (non-subscriber, missing nodes)
- MusicLibrary.HttpError default status-kind mapping
- Discogs.API.ErrorResponse fallback message and retry-delay behavior
- ArtistRefreshWikipediaData {:cancel, :no_english_wikipedia} worker path
- StatsComponents grouped on-this-day records and anniversary labels

test/music_brainz/release_search_result_test.exs

@@ -2,4 +2,122 @@ defmodule MusicBrainz.ReleaseSearchResultTest do
   use ExUnit.Case, async: true
 
   doctest MusicBrainz.ReleaseSearchResult
+
+  alias MusicBrainz.ReleaseSearchResult
+
+  describe "from_api_response/1" do
+    test "handles missing release-group" do
+      r = %{
+        "id" => "rel-1",
+        "title" => "No Release Group",
+        "artist-credit" => [
+          %{"artist" => %{"name" => "Artist Name"}}
+        ],
+        "date" => "2020-01-01",
+        "barcode" => "1234",
+        "media" => [%{"format" => "CD", "track-count" => 10, "disc-count" => 1}]
+      }
+
+      result = ReleaseSearchResult.from_api_response(r)
+      assert result.id == "rel-1"
+      assert result.release_group == nil
+      assert result.artists == "Artist Name"
+    end
+
+    test "handles missing artist-credit" do
+      r = %{
+        "id" => "rel-2",
+        "title" => "No Artists",
+        "release-group" => %{
+          "id" => "rg-1",
+          "primary-type" => "Album",
+          "title" => "The Album"
+        },
+        "date" => nil,
+        "barcode" => nil,
+        "media" => []
+      }
+
+      result = ReleaseSearchResult.from_api_response(r)
+      assert result.artists == ""
+      assert result.release_group.type == :album
+    end
+  end
+
+  describe "format/1" do
+    test "returns :unknown for nil media format" do
+      result = %ReleaseSearchResult{
+        id: "1",
+        title: "T",
+        release_group: nil,
+        artists: "A",
+        date: "2000",
+        barcode: "0",
+        media: [%{format: nil, disc_count: 0, track_count: 5}]
+      }
+
+      assert ReleaseSearchResult.format(result) == :unknown
+    end
+
+    test "returns :unknown for completely unknown format string" do
+      result = %ReleaseSearchResult{
+        id: "1",
+        title: "T",
+        release_group: nil,
+        artists: "A",
+        date: "2000",
+        barcode: "0",
+        media: [%{format: "Wax Cylinder", disc_count: 0, track_count: 4}]
+      }
+
+      assert ReleaseSearchResult.format(result) == :unknown
+    end
+
+    test "returns :multi for empty media list" do
+      result = %ReleaseSearchResult{
+        id: "1",
+        title: "T",
+        release_group: nil,
+        artists: "A",
+        date: "2000",
+        barcode: "0",
+        media: []
+      }
+
+      # Empty media list has no frequencies, so the catch-all returns :multi
+      assert ReleaseSearchResult.format(result) == :multi
+    end
+
+    test "returns :multi for mixed format types" do
+      result = %ReleaseSearchResult{
+        id: "1",
+        title: "T",
+        release_group: nil,
+        artists: "A",
+        date: "2000",
+        barcode: "0",
+        media: [
+          %{format: "CD", disc_count: 1, track_count: 10},
+          %{format: "12\" Vinyl", disc_count: 1, track_count: 6},
+          %{format: "Digital Media", disc_count: 0, track_count: 12}
+        ]
+      }
+
+      assert ReleaseSearchResult.format(result) == :multi
+    end
+  end
+
+  describe "parse_media/1" do
+    test "handles empty media list" do
+      assert ReleaseSearchResult.parse_media([]) == []
+    end
+
+    test "handles missing fields gracefully" do
+      media = [%{}]
+      parsed = ReleaseSearchResult.parse_media(media)
+      assert hd(parsed).format == nil
+      assert hd(parsed).track_count == nil
+      assert hd(parsed).disc_count == nil
+    end
+  end
 end