don't include empty tracks in slack summary

lib/pears/slack/messages/daily_pears_message.ex

@@ -7,6 +7,7 @@ defmodule Pears.Slack.Messages.DailyPairsMessage do
     summary_lines =
       team.tracks
       |> Map.values()
+      |> Enum.filter(fn track -> map_size(track.pears) > 0 end)
       |> Enum.map(&build_daily_pears_summary_line/1)
       |> Enum.join("\n")
       |> String.trim_trailing()

test/pears/slack/messages/daily_pears_message_test.exs

@@ -0,0 +1,78 @@
+defmodule Pears.Slack.Messages.DailyPairsMessageTest do
+  use ExUnit.Case, async: true
+
+  alias Pears.Core.Team
+  alias Pears.Slack.Messages.DailyPairsMessage
+
+  setup [:team]
+
+  describe "new/1" do
+    test "returns a message with a list of pairs", %{team: team} do
+      team =
+        team
+        |> Team.add_track("track1")
+        |> Team.add_pear("pear1")
+        |> Team.add_pear("pear2")
+        |> Team.add_pear_to_track("pear1", "track1")
+        |> Team.add_pear_to_track("pear2", "track1")
+        |> Team.add_track("track2")
+        |> Team.add_pear("pear3")
+        |> Team.add_pear("pear4")
+        |> Team.add_pear_to_track("pear3", "track2")
+        |> Team.add_pear_to_track("pear4", "track2")
+
+      {:ok, message} = DailyPairsMessage.new(team)
+
+      assert lines(message) == [
+               "Today's 🍐s are:",
+               "- pear1 & pear2 on track1",
+               "- pear3 & pear4 on track2"
+             ]
+    end
+
+    test "does not include empty tracks", %{team: team} do
+      team =
+        team
+        |> Team.add_track("track1")
+        |> Team.add_pear("pear1")
+        |> Team.add_pear("pear2")
+        |> Team.add_pear_to_track("pear1", "track1")
+        |> Team.add_pear_to_track("pear2", "track1")
+        |> Team.add_track("track2")
+
+      {:ok, message} = DailyPairsMessage.new(team)
+
+      assert lines(message) == [
+               "Today's 🍐s are:",
+               "- pear1 & pear2 on track1"
+             ]
+    end
+
+    test "does not include available pears", %{team: team} do
+      team =
+        team
+        |> Team.add_track("track1")
+        |> Team.add_pear("pear1")
+        |> Team.add_pear("pear2")
+        |> Team.add_pear_to_track("pear1", "track1")
+
+      {:ok, message} = DailyPairsMessage.new(team)
+
+      assert lines(message) == [
+               "Today's 🍐s are:",
+               "- pear1 on track1"
+             ]
+    end
+  end
+
+  defp team(_) do
+    {:ok, team: Team.new(name: "test team")}
+  end
+
+  defp lines(message) do
+    message
+    |> String.trim()
+    |> String.split("\n")
+    |> Enum.map(&String.trim/1)
+  end
+end