Use websockets on stats page to determine which match to stat.

test/integration/mat_stats_live_updates_test.rb

@@ -0,0 +1,37 @@
+require "test_helper"
+
+class MatStatsLiveUpdatesTest < ActionDispatch::IntegrationTest
+  include ActionView::RecordIdentifier
+
+  test "destroying all matches broadcasts no-match state for mat stats stream" do
+    create_double_elim_tournament_single_weight_1_6(4)
+    mat = @tournament.mats.create!(name: "Mat 1")
+    @tournament.reset_and_fill_bout_board
+    stream = stream_name_for(mat)
+
+    clear_streams(stream)
+    @tournament.destroy_all_matches
+
+    assert_operator broadcasts_for(stream).size, :>, 0
+    payload = broadcasts_for(stream).last
+    assert_includes payload, dom_id(mat, :current_match)
+    assert_includes payload, "No matches assigned to this mat."
+  end
+
+  private
+
+  def broadcasts_for(stream)
+    ActionCable.server.pubsub.broadcasts(stream)
+  end
+
+  def clear_streams(*streams)
+    ActionCable.server.pubsub.clear
+    streams.each do |stream|
+      broadcasts_for(stream).clear
+    end
+  end
+
+  def stream_name_for(streamable)
+    Turbo::StreamsChannel.send(:stream_name_from, [streamable])
+  end
+end