diff --git a/lib/music_brainz/release_search_result.ex b/lib/music_brainz/release_search_result.ex
index b43d18b6..c4ea06eb 100644
--- a/lib/music_brainz/release_search_result.ex
+++ b/lib/music_brainz/release_search_result.ex
@@ -16,6 +16,44 @@ defmodule MusicBrainz.ReleaseSearchResult do
     }
   end
 
+  @doc """
+  Returns the physical format of a release based on its media.
+
+  Returns `:multi` when a release contains different format types.
+
+  ## Examples
+
+      iex> MusicBrainz.ReleaseSearchResult.format(%MusicBrainz.ReleaseSearchResult{
+      ...>   id: "1", title: "T", release_group: nil, artists: "A", date: "2000", barcode: "0",
+      ...>   media: [%{format: "CD", disc_count: 1, track_count: 11}]
+      ...> })
+      :cd
+
+      iex> MusicBrainz.ReleaseSearchResult.format(%MusicBrainz.ReleaseSearchResult{
+      ...>   id: "1", title: "T", release_group: nil, artists: "A", date: "2000", barcode: "0",
+      ...>   media: [%{format: "12\\" Vinyl", disc_count: 0, track_count: 8}]
+      ...> })
+      :vinyl
+
+      iex> MusicBrainz.ReleaseSearchResult.format(%MusicBrainz.ReleaseSearchResult{
+      ...>   id: "1", title: "T", release_group: nil, artists: "A", date: "2000", barcode: "0",
+      ...>   media: [
+      ...>     %{format: "CD", disc_count: 1, track_count: 10},
+      ...>     %{format: "CD", disc_count: 1, track_count: 9}
+      ...>   ]
+      ...> })
+      :cd
+
+      iex> MusicBrainz.ReleaseSearchResult.format(%MusicBrainz.ReleaseSearchResult{
+      ...>   id: "1", title: "T", release_group: nil, artists: "A", date: "2000", barcode: "0",
+      ...>   media: [
+      ...>     %{format: "CD", disc_count: 0, track_count: 11},
+      ...>     %{format: "DVD-Video", disc_count: 0, track_count: 22}
+      ...>   ]
+      ...> })
+      :multi
+
+  """
   def format(release_search_result) do
     sorted_frequencies =
       release_search_result.media
diff --git a/lib/music_library/country.ex b/lib/music_library/country.ex
index 998787f1..de393a92 100644
--- a/lib/music_library/country.ex
+++ b/lib/music_library/country.ex
@@ -276,12 +276,45 @@ defmodule MusicLibrary.Country do
       iex> MusicLibrary.Country.to_emoji("US")
       "🇺🇸"
 
+      iex> MusicLibrary.Country.to_emoji("PL")
+      "🇵🇱"
+
+      iex> MusicLibrary.Country.to_emoji("GB")
+      "🇬🇧"
+
+      iex> MusicLibrary.Country.to_emoji("us")
+      "🇺🇸"
+
+      iex> MusicLibrary.Country.to_emoji("pl")
+      "🇵🇱"
+
       iex> MusicLibrary.Country.to_emoji("GB-SCT")
       "🏴󠁧󠁢󠁳󠁣󠁴󠁿"
 
+      iex> MusicLibrary.Country.to_emoji("GB-WLS")
+      "🏴󠁧󠁢󠁷󠁬󠁳󠁿"
+
+      iex> MusicLibrary.Country.to_emoji("GB-ENG")
+      "🏴󠁧󠁢󠁥󠁮󠁧󠁿"
+
+      iex> MusicLibrary.Country.to_emoji("GB-CYM") == MusicLibrary.Country.to_emoji("GB-WLS")
+      true
+
       iex> MusicLibrary.Country.to_emoji("USA")
       "🇺🇸"
 
+      iex> MusicLibrary.Country.to_emoji("GBR")
+      "🇬🇧"
+
+      iex> MusicLibrary.Country.to_emoji("POL")
+      "🇵🇱"
+
+      iex> MusicLibrary.Country.to_emoji("en-US")
+      "🇺🇸"
+
+      iex> MusicLibrary.Country.to_emoji("pl-PL")
+      "🇵🇱"
+
   """
   @spec to_emoji(String.t()) :: String.t()
   def to_emoji(code) when is_binary(code) do
diff --git a/lib/music_library_web/duration.ex b/lib/music_library_web/duration.ex
index 301c29c1..e609b0d4 100644
--- a/lib/music_library_web/duration.ex
+++ b/lib/music_library_web/duration.ex
@@ -1,4 +1,26 @@
 defmodule MusicLibraryWeb.Duration do
+  @moduledoc """
+  Formats durations from milliseconds to human-readable strings.
+  """
+
+  @doc """
+  Formats a duration in milliseconds as a human-readable string.
+
+  ## Examples
+
+      iex> MusicLibraryWeb.Duration.format_duration(30_000)
+      "0:30"
+
+      iex> MusicLibraryWeb.Duration.format_duration(90_000)
+      "1:30"
+
+      iex> MusicLibraryWeb.Duration.format_duration(3_723_000)
+      "1:02:03"
+
+      iex> MusicLibraryWeb.Duration.format_duration(0)
+      "0:00"
+
+  """
   def format_duration(milliseconds) do
     milliseconds
     |> System.convert_time_unit(:millisecond, :second)
diff --git a/test/last_fm/session_test.exs b/test/last_fm/session_test.exs
index d3cd8ec8..98f7c649 100644
--- a/test/last_fm/session_test.exs
+++ b/test/last_fm/session_test.exs
@@ -1,26 +1,5 @@
 defmodule LastFm.SessionTest do
   use ExUnit.Case, async: true
 
-  alias LastFm.Session
-
   doctest LastFm.Session
-
-  @xml """
-  <?xml version="1.0" encoding="UTF-8"?>
-  <lfm status="ok">
-    <session>
-      <name>cloud8421</name>
-      <key>super-secret</key>
-      <subscriber>1</subscriber>
-    </session>
-  </lfm>
-  """
-
-  test "parse/1" do
-    assert %Session{
-             name: "cloud8421",
-             key: "super-secret",
-             pro: true
-           } == Session.parse(@xml)
-  end
 end
diff --git a/test/music_brainz/release_search_result_test.exs b/test/music_brainz/release_search_result_test.exs
index 8f6f2e94..1792fdaf 100644
--- a/test/music_brainz/release_search_result_test.exs
+++ b/test/music_brainz/release_search_result_test.exs
@@ -1,79 +1,5 @@
 defmodule MusicBrainz.ReleaseSearchResultTest do
   use ExUnit.Case, async: true
 
-  alias MusicBrainz.ReleaseSearchResult
-
-  @single_cd %MusicBrainz.ReleaseSearchResult{
-    id: "dc393148-be34-4056-be66-b2b95905c5c1",
-    title: "Equally Cursed and Blessed",
-    release_group: %{
-      id: "c35fc446-65cc-3645-939b-1b3782e60639",
-      type: :album,
-      title: "Equally Cursed and Blessed"
-    },
-    artists: "Catatonia",
-    date: "1999-04-12",
-    barcode: "639842709422",
-    media: [%{format: "CD", disc_count: 5, track_count: 11}]
-  }
-
-  @double_cd %MusicBrainz.ReleaseSearchResult{
-    id: "51ebc32b-d21f-4466-9297-94b6a3e0e6ba",
-    title: "Rock in Rio",
-    release_group: %{
-      id: "ea6dac58-887a-35a8-86ff-08c56e6bf047",
-      type: :album,
-      title: "Rock in Rio"
-    },
-    artists: "Iron Maiden",
-    date: "2002-03-21",
-    barcode: "724353864309",
-    media: [
-      %{format: "CD", disc_count: 1, track_count: 10},
-      %{format: "CD", disc_count: 1, track_count: 9}
-    ]
-  }
-
-  @single_vinyl %MusicBrainz.ReleaseSearchResult{
-    id: "3af1f610-9df1-4a48-8874-78cd64e25888",
-    title: "Somewhere in Time",
-    release_group: %{
-      id: "a5fe4d2d-3aab-3e86-91ad-22a3fe16c4f2",
-      type: :album,
-      title: "Somewhere in Time"
-    },
-    artists: "Iron Maiden",
-    date: "1986-09-29",
-    barcode: "5099924059718",
-    media: [%{format: "12\" Vinyl", disc_count: 0, track_count: 8}]
-  }
-
-  @multi %MusicBrainz.ReleaseSearchResult{
-    id: "804e4781-bc17-496e-8abd-d61c7173391c",
-    title: "Live With the Plovdiv Psychotic Symphony",
-    release_group: %{
-      id: "887898c3-ef40-4162-88d3-1fbc58ee2d09",
-      type: :album,
-      title: "Live With the Plovdiv Psychotic Symphony"
-    },
-    artists: "Sons of Apollo, Пловдивска филхармония",
-    date: "2019-08-30",
-    barcode: "190759669228",
-    media: [
-      %{format: "CD", disc_count: 0, track_count: 11},
-      %{format: "CD", disc_count: 1, track_count: 10},
-      %{format: "CD", disc_count: 0, track_count: 3},
-      %{format: "DVD-Video", disc_count: 0, track_count: 22},
-      %{format: "Blu-ray", disc_count: 0, track_count: 42}
-    ]
-  }
-
-  describe "format/1" do
-    test "it returns the format of the release" do
-      assert ReleaseSearchResult.format(@single_cd) == :cd
-      assert ReleaseSearchResult.format(@single_vinyl) == :vinyl
-      assert ReleaseSearchResult.format(@double_cd) == :cd
-      assert ReleaseSearchResult.format(@multi) == :multi
-    end
-  end
+  doctest MusicBrainz.ReleaseSearchResult
 end
diff --git a/test/music_library/country_test.exs b/test/music_library/country_test.exs
index bb1d82d7..f08d1094 100644
--- a/test/music_library/country_test.exs
+++ b/test/music_library/country_test.exs
@@ -1,39 +1,5 @@
 defmodule MusicLibrary.CountryTest do
   use ExUnit.Case, async: true
 
-  alias MusicLibrary.Country
-
-  describe "to_emoji/1" do
-    test "converts alpha-2 codes" do
-      assert Country.to_emoji("US") == "🇺🇸"
-      assert Country.to_emoji("PL") == "🇵🇱"
-      assert Country.to_emoji("GB") == "🇬🇧"
-    end
-
-    test "is case insensitive" do
-      assert Country.to_emoji("us") == "🇺🇸"
-      assert Country.to_emoji("pl") == "🇵🇱"
-    end
-
-    test "converts subdivision codes" do
-      assert Country.to_emoji("GB-SCT") == "🏴󠁧󠁢󠁳󠁣󠁴󠁿"
-      assert Country.to_emoji("GB-WLS") == "🏴󠁧󠁢󠁷󠁬󠁳󠁿"
-      assert Country.to_emoji("GB-ENG") == "🏴󠁧󠁢󠁥󠁮󠁧󠁿"
-    end
-
-    test "maps GB-CYM to GB-WLS" do
-      assert Country.to_emoji("GB-CYM") == Country.to_emoji("GB-WLS")
-    end
-
-    test "converts alpha-3 codes" do
-      assert Country.to_emoji("USA") == "🇺🇸"
-      assert Country.to_emoji("GBR") == "🇬🇧"
-      assert Country.to_emoji("POL") == "🇵🇱"
-    end
-
-    test "converts IETF language tags" do
-      assert Country.to_emoji("en-US") == "🇺🇸"
-      assert Country.to_emoji("pl-PL") == "🇵🇱"
-    end
-  end
+  doctest MusicLibrary.Country
 end
diff --git a/test/music_library_web/duration_test.exs b/test/music_library_web/duration_test.exs
new file mode 100644
index 00000000..0abd3aaa
--- /dev/null
+++ b/test/music_library_web/duration_test.exs
@@ -0,0 +1,5 @@
+defmodule MusicLibraryWeb.DurationTest do
+  use ExUnit.Case, async: true
+
+  doctest MusicLibraryWeb.Duration
+end