diff --git a/apps/examples/test/examples/log_trade/advisor_test.exs b/apps/examples/test/examples/log_trade/advisor_test.exs
new file mode 100644
index 000000000..6a227956e
--- /dev/null
+++ b/apps/examples/test/examples/log_trade/advisor_test.exs
@@ -0,0 +1,28 @@
+defmodule Examples.LogTrade.AdvisorTest do
+  use Tai.TestSupport.E2ECase, async: false
+
+  @scenario :log_trade
+  @venue :test_exchange_a
+  @product :btc_usd
+
+  def before_start_app, do: seed_mock_responses(@scenario)
+
+  def after_start_app, do: seed_venues(@scenario)
+
+  def after_boot_app do
+    start_venue(@venue)
+    configure_fleet(@scenario)
+    start_advisors(where: [fleet_id: @scenario])
+  end
+
+  test "logs the bid/ask spread via a custom event" do
+    push_stream_market_data({@scenario, :snapshot, @venue, @product})
+
+    assert_receive {TaiEvents.Event, %Examples.LogSpread.Events.Spread{} = event, _}
+    assert event.venue_id == @venue
+    assert event.product_symbol == @product
+    assert event.bid_price == Decimal.new("6500.1")
+    assert event.ask_price == Decimal.new("6500.11")
+    assert event.spread == Decimal.new("0.01")
+  end
+end
diff --git a/apps/tai/lib/tai/system_bus.ex b/apps/tai/lib/tai/system_bus.ex
index e0e215178..41d42ba5e 100644
--- a/apps/tai/lib/tai/system_bus.ex
+++ b/apps/tai/lib/tai/system_bus.ex
@@ -1,5 +1,16 @@
 defmodule Tai.SystemBus do
+  @moduledoc """
+  A core pubsub bus for async message communication. The following subsystems depend on this module.
+
+  - boot
+  - metrics
+
+  NOTE: This module should not be used as a public API as it is subject to change
+  """
+
   @type partitions :: pos_integer
+  @type topic :: atom | tuple
+  @type topics :: [topic]
 
   @spec child_spec(opts :: term) :: Supervisor.child_spec()
   def child_spec(opts) do
@@ -21,6 +32,9 @@ defmodule Tai.SystemBus do
     )
   end
 
+  @spec subscribe(topic | topics) :: :ok
+  def subscribe(topics)
+
   def subscribe([]), do: :ok
 
   def subscribe([topic | tail]) do
@@ -34,6 +48,9 @@ defmodule Tai.SystemBus do
     |> subscribe
   end
 
+  @spec unsubscribe(topic | topics) :: :ok
+  def unsubscribe(topics)
+
   def unsubscribe([]), do: :ok
 
   def unsubscribe([topic | tail]) do
@@ -47,6 +64,7 @@ defmodule Tai.SystemBus do
     |> unsubscribe
   end
 
+  @spec broadcast(topic, term) :: :ok
   def broadcast(topic, message) do
     Registry.dispatch(__MODULE__, topic, fn entries ->
       for {pid, _} <- entries, do: send(pid, message)