test: cover repo_listener

10 characterization tests for PostgreSQL NOTIFY → PubSub relay:
contact_status_changed channel → db:contact_status topic, oban_job_changed
→ db:oban_jobs, channel isolation, invalid JSON silent-swallow, catch-all
handling of unknown channels and info messages.

test/microwaveprop/repo_listener_test.exs

@@ -0,0 +1,137 @@
+defmodule Microwaveprop.RepoListenerTest do
+  @moduledoc """
+  Characterization tests for `Microwaveprop.RepoListener`.
+
+  The module is a GenServer that subscribes to two PostgreSQL `NOTIFY`
+  channels via `Postgrex.Notifications` and rebroadcasts decoded
+  payloads via `Phoenix.PubSub`. These tests exercise the `handle_info/2`
+  seam directly using the exact message shape `Postgrex.Notifications`
+  delivers — no database connection required.
+  """
+
+  use ExUnit.Case, async: false
+
+  alias Microwaveprop.RepoListener
+
+  # Shape of the message that `Postgrex.Notifications` delivers to a
+  # listening process. Ref. https://hexdocs.pm/postgrex/Postgrex.Notifications.html
+  defp notification(channel, payload) do
+    {:notification, self(), make_ref(), channel, payload}
+  end
+
+  describe "handle_info/2 — contact_status_changed" do
+    setup do
+      :ok = Phoenix.PubSub.subscribe(Microwaveprop.PubSub, "db:contact_status")
+      on_exit(fn -> Phoenix.PubSub.unsubscribe(Microwaveprop.PubSub, "db:contact_status") end)
+      :ok
+    end
+
+    test "broadcasts decoded payload on db:contact_status topic" do
+      payload = Jason.encode!(%{"contact_id" => "abc-123", "status" => "queued"})
+      msg = notification("contact_status_changed", payload)
+
+      assert {:noreply, %{pid: nil}} = RepoListener.handle_info(msg, %{pid: nil})
+
+      assert_receive {:contact_status_changed, %{"contact_id" => "abc-123", "status" => "queued"}}
+    end
+
+    test "preserves full decoded payload structure (nested maps/lists)" do
+      data = %{
+        "contact_id" => "xyz",
+        "fields" => ["weather", "hrrr"],
+        "meta" => %{"source" => "notify"}
+      }
+
+      msg = notification("contact_status_changed", Jason.encode!(data))
+
+      assert {:noreply, _} = RepoListener.handle_info(msg, %{pid: nil})
+      assert_receive {:contact_status_changed, ^data}
+    end
+
+    test "silently ignores invalid JSON payload" do
+      msg = notification("contact_status_changed", "not-json-at-all{")
+
+      assert {:noreply, %{pid: nil}} = RepoListener.handle_info(msg, %{pid: nil})
+      refute_receive {:contact_status_changed, _}, 50
+    end
+  end
+
+  describe "handle_info/2 — oban_job_changed" do
+    setup do
+      :ok = Phoenix.PubSub.subscribe(Microwaveprop.PubSub, "db:oban_jobs")
+      on_exit(fn -> Phoenix.PubSub.unsubscribe(Microwaveprop.PubSub, "db:oban_jobs") end)
+      :ok
+    end
+
+    test "broadcasts decoded payload on db:oban_jobs topic" do
+      payload = Jason.encode!(%{"id" => 42, "state" => "completed", "queue" => "weather"})
+      msg = notification("oban_job_changed", payload)
+
+      assert {:noreply, %{pid: nil}} = RepoListener.handle_info(msg, %{pid: nil})
+
+      assert_receive {:oban_job_changed, %{"id" => 42, "state" => "completed", "queue" => "weather"}}
+    end
+
+    test "silently ignores invalid JSON payload" do
+      msg = notification("oban_job_changed", "{\"broken\":")
+
+      assert {:noreply, %{pid: nil}} = RepoListener.handle_info(msg, %{pid: nil})
+      refute_receive {:oban_job_changed, _}, 50
+    end
+  end
+
+  describe "handle_info/2 — channel isolation" do
+    test "contact_status_changed does not broadcast on db:oban_jobs" do
+      :ok = Phoenix.PubSub.subscribe(Microwaveprop.PubSub, "db:oban_jobs")
+      on_exit(fn -> Phoenix.PubSub.unsubscribe(Microwaveprop.PubSub, "db:oban_jobs") end)
+
+      msg = notification("contact_status_changed", Jason.encode!(%{"contact_id" => "abc"}))
+
+      assert {:noreply, _} = RepoListener.handle_info(msg, %{pid: nil})
+      refute_receive {:oban_job_changed, _}, 50
+      refute_receive {:contact_status_changed, _}, 50
+    end
+
+    test "oban_job_changed does not broadcast on db:contact_status" do
+      :ok = Phoenix.PubSub.subscribe(Microwaveprop.PubSub, "db:contact_status")
+      on_exit(fn -> Phoenix.PubSub.unsubscribe(Microwaveprop.PubSub, "db:contact_status") end)
+
+      msg = notification("oban_job_changed", Jason.encode!(%{"id" => 1}))
+
+      assert {:noreply, _} = RepoListener.handle_info(msg, %{pid: nil})
+      refute_receive {:contact_status_changed, _}, 50
+      refute_receive {:oban_job_changed, _}, 50
+    end
+  end
+
+  describe "handle_info/2 — unknown / unrelated messages" do
+    test "ignores notifications on unknown channels without crashing" do
+      :ok = Phoenix.PubSub.subscribe(Microwaveprop.PubSub, "db:contact_status")
+      :ok = Phoenix.PubSub.subscribe(Microwaveprop.PubSub, "db:oban_jobs")
+
+      on_exit(fn ->
+        Phoenix.PubSub.unsubscribe(Microwaveprop.PubSub, "db:contact_status")
+        Phoenix.PubSub.unsubscribe(Microwaveprop.PubSub, "db:oban_jobs")
+      end)
+
+      msg = notification("some_other_channel", Jason.encode!(%{"x" => 1}))
+
+      assert {:noreply, %{pid: nil}} = RepoListener.handle_info(msg, %{pid: nil})
+      refute_receive {:contact_status_changed, _}, 50
+      refute_receive {:oban_job_changed, _}, 50
+    end
+
+    test "ignores arbitrary info messages without crashing" do
+      assert {:noreply, %{pid: nil}} = RepoListener.handle_info(:random_message, %{pid: nil})
+      assert {:noreply, %{pid: nil}} = RepoListener.handle_info({:foo, :bar}, %{pid: nil})
+    end
+
+    test "returns state unchanged regardless of message" do
+      state = %{pid: nil, extra: :keep_me}
+      assert {:noreply, ^state} = RepoListener.handle_info(:whatever, state)
+
+      msg = notification("contact_status_changed", Jason.encode!(%{"a" => 1}))
+      assert {:noreply, ^state} = RepoListener.handle_info(msg, state)
+    end
+  end
+end