diff --git a/test/music_library/scrobble_activity_test.exs b/test/music_library/scrobble_activity_test.exs
new file mode 100644
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+++ b/test/music_library/scrobble_activity_test.exs
@@ -0,0 +1,290 @@
+defmodule MusicLibrary.ScrobbleActivityTest do
+  @moduledoc false
+
+  use MusicLibrary.DataCase
+
+  alias MusicBrainz.Fixtures.Release, as: ReleaseFixtures
+  alias MusicBrainz.Release
+  alias MusicBrainz.Release.{Artist, Medium, Track}
+  alias MusicLibrary.ScrobbleActivity
+  alias MusicLibrary.Secrets
+
+  @release ReleaseFixtures.release_with_media(:marbles) |> Release.from_api_response()
+
+  defp store_session_key(_) do
+    Secrets.store("last_fm_session_key", "test_session_key")
+    :ok
+  end
+
+  defp stub_lastfm_success(_) do
+    Req.Test.stub(LastFm.API, fn conn ->
+      Req.Test.json(conn, %{"scrobbles" => %{"@attr" => %{"accepted" => 1}}})
+    end)
+
+    :ok
+  end
+
+  describe "can_scrobble?/0" do
+    test "returns false when no session key is stored" do
+      refute ScrobbleActivity.can_scrobble?()
+    end
+
+    test "returns true when session key exists" do
+      Secrets.store("last_fm_session_key", "test_session_key")
+      assert ScrobbleActivity.can_scrobble?()
+    end
+  end
+
+  describe "scrobble_release/3" do
+    setup [:store_session_key, :stub_lastfm_success]
+
+    test "scrobbles all tracks with :started_at" do
+      started_at = DateTime.utc_now()
+      assert {:ok, _} = ScrobbleActivity.scrobble_release(@release, :started_at, started_at)
+    end
+
+    test "scrobbles all tracks with :finished_at" do
+      finished_at = DateTime.utc_now()
+      assert {:ok, _} = ScrobbleActivity.scrobble_release(@release, :finished_at, finished_at)
+    end
+
+    test "returns error when release has zero duration" do
+      zero_duration_release = %{@release | media: [%{tracks: [%{length: 0}]}]}
+      started_at = DateTime.utc_now()
+
+      assert {:error, :no_duration} =
+               ScrobbleActivity.scrobble_release(zero_duration_release, :started_at, started_at)
+    end
+  end
+
+  describe "scrobble_release/3 without session key" do
+    setup [:stub_lastfm_success]
+
+    test "returns error" do
+      started_at = DateTime.utc_now()
+
+      assert {:error, :no_session_key} =
+               ScrobbleActivity.scrobble_release(@release, :started_at, started_at)
+    end
+  end
+
+  describe "scrobble_medium/4" do
+    setup [:store_session_key, :stub_lastfm_success]
+
+    test "scrobbles tracks from a specific medium with :started_at" do
+      started_at = DateTime.utc_now()
+      assert {:ok, _} = ScrobbleActivity.scrobble_medium(1, @release, :started_at, started_at)
+    end
+
+    test "scrobbles tracks from a specific medium with :finished_at" do
+      finished_at = DateTime.utc_now()
+      assert {:ok, _} = ScrobbleActivity.scrobble_medium(1, @release, :finished_at, finished_at)
+    end
+
+    test "returns error when medium not found" do
+      started_at = DateTime.utc_now()
+
+      assert {:error, :medium_not_found} =
+               ScrobbleActivity.scrobble_medium(99, @release, :started_at, started_at)
+    end
+
+    test "returns error when medium not found with :finished_at" do
+      finished_at = DateTime.utc_now()
+
+      assert {:error, :medium_not_found} =
+               ScrobbleActivity.scrobble_medium(99, @release, :finished_at, finished_at)
+    end
+
+    test "returns error when medium has zero duration" do
+      zero_duration_medium = %Medium{
+        title: "",
+        format: "CD",
+        number: 1,
+        track_count: 1,
+        tracks: [
+          %Track{id: "t1", title: "Silent", length: 0, artists: [], number: "1", position: 1}
+        ]
+      }
+
+      release = %{@release | media: [zero_duration_medium]}
+      started_at = DateTime.utc_now()
+
+      assert {:error, :no_duration} =
+               ScrobbleActivity.scrobble_medium(1, release, :started_at, started_at)
+    end
+  end
+
+  describe "scrobble_medium/4 without session key" do
+    setup [:stub_lastfm_success]
+
+    test "returns error" do
+      started_at = DateTime.utc_now()
+
+      assert {:error, :no_session_key} =
+               ScrobbleActivity.scrobble_medium(1, @release, :started_at, started_at)
+    end
+  end
+
+  describe "scrobble_tracks/4" do
+    setup [:store_session_key, :stub_lastfm_success]
+
+    setup do
+      track_ids =
+        @release
+        |> Release.tracks()
+        |> Enum.take(2)
+        |> Enum.map(& &1.id)
+        |> MapSet.new()
+
+      %{track_ids: track_ids}
+    end
+
+    test "scrobbles selected tracks with :started_at", %{track_ids: track_ids} do
+      started_at = DateTime.utc_now()
+
+      assert {:ok, _} =
+               ScrobbleActivity.scrobble_tracks(track_ids, @release, :started_at, started_at)
+    end
+
+    test "scrobbles selected tracks with :finished_at", %{track_ids: track_ids} do
+      finished_at = DateTime.utc_now()
+
+      assert {:ok, _} =
+               ScrobbleActivity.scrobble_tracks(track_ids, @release, :finished_at, finished_at)
+    end
+
+    test "returns error when no tracks selected" do
+      started_at = DateTime.utc_now()
+
+      assert {:error, :no_duration} =
+               ScrobbleActivity.scrobble_tracks(MapSet.new(), @release, :started_at, started_at)
+    end
+
+    test "returns error when selected tracks have zero length" do
+      zero_track = %Track{
+        id: "zero",
+        title: "Silent",
+        length: 0,
+        artists: [],
+        number: "1",
+        position: 1
+      }
+
+      release = %{
+        @release
+        | media: [
+            %Medium{title: "", format: "CD", number: 1, track_count: 1, tracks: [zero_track]}
+          ]
+      }
+
+      started_at = DateTime.utc_now()
+
+      assert {:error, :no_duration} =
+               ScrobbleActivity.scrobble_tracks(
+                 MapSet.new(["zero"]),
+                 release,
+                 :started_at,
+                 started_at
+               )
+    end
+  end
+
+  describe "scrobble_tracks/4 without session key" do
+    setup [:stub_lastfm_success]
+
+    test "returns error" do
+      track_ids =
+        @release
+        |> Release.tracks()
+        |> Enum.take(1)
+        |> Enum.map(& &1.id)
+        |> MapSet.new()
+
+      started_at = DateTime.utc_now()
+
+      assert {:error, :no_session_key} =
+               ScrobbleActivity.scrobble_tracks(track_ids, @release, :started_at, started_at)
+    end
+  end
+
+  describe "scrobble construction" do
+    setup [:store_session_key]
+
+    test "populates correct fields and increments timestamps" do
+      started_at = ~U[2024-01-01 12:00:00Z]
+
+      Req.Test.stub(LastFm.API, fn conn ->
+        {:ok, body, conn} = Plug.Conn.read_body(conn)
+        params = URI.decode_query(body)
+
+        # First track should have timestamp = started_at + track length
+        first_track = Enum.at(Release.tracks(@release), 0)
+        expected_timestamp = DateTime.add(started_at, first_track.length, :millisecond)
+
+        assert params["track[0]"] == first_track.title
+        assert params["artist[0]"] == first_track.artists |> List.first() |> Map.get(:name)
+        assert params["album[0]"] == @release.title
+        assert params["timestamp[0]"] == Integer.to_string(DateTime.to_unix(expected_timestamp))
+
+        Req.Test.json(conn, %{"scrobbles" => %{"@attr" => %{"accepted" => 1}}})
+      end)
+
+      assert {:ok, _} = ScrobbleActivity.scrobble_release(@release, :started_at, started_at)
+    end
+
+    test "sets album_artist when track artist differs from release artist" do
+      different_artist = %Artist{id: "a2", name: "Guest Artist", sort_name: "Guest"}
+
+      track = %Track{
+        id: "t1",
+        title: "Collab",
+        length: 60_000,
+        artists: [different_artist],
+        number: "1",
+        position: 1
+      }
+
+      medium = %Medium{title: "", format: "CD", number: 1, track_count: 1, tracks: [track]}
+      release = %{@release | media: [medium]}
+
+      Req.Test.stub(LastFm.API, fn conn ->
+        {:ok, body, conn} = Plug.Conn.read_body(conn)
+        params = URI.decode_query(body)
+
+        release_artist = @release.artists |> List.first() |> Map.get(:name)
+        assert params["album_artist[0]"] == release_artist
+
+        Req.Test.json(conn, %{"scrobbles" => %{"@attr" => %{"accepted" => 1}}})
+      end)
+
+      assert {:ok, _} =
+               ScrobbleActivity.scrobble_release(release, :started_at, ~U[2024-01-01 12:00:00Z])
+    end
+
+    test "does not set album_artist when track artist matches release artist" do
+      track_ids =
+        @release
+        |> Release.tracks()
+        |> Enum.take(1)
+        |> Enum.map(& &1.id)
+        |> MapSet.new()
+
+      Req.Test.stub(LastFm.API, fn conn ->
+        {:ok, body, conn} = Plug.Conn.read_body(conn)
+        params = URI.decode_query(body)
+
+        refute Map.has_key?(params, "album_artist[0]")
+
+        Req.Test.json(conn, %{"scrobbles" => %{"@attr" => %{"accepted" => 1}}})
+      end)
+
+      assert {:ok, _} =
+               ScrobbleActivity.scrobble_tracks(
+                 track_ids,
+                 @release,
+                 :started_at,
+                 ~U[2024-01-01 12:00:00Z]
+               )
+    end
+  end
+end