Add FETestHelpers.HeartbeatTracker.count/1

This makes it straight forward to get the count of heartbeats recorded
on each tracker.

Author: aaronrenner

fe_test_helpers/lib/fe_test_helpers/heartbeat_tracker.ex

@@ -20,6 +20,13 @@ defmodule FETestHelpers.HeartbeatTracker do
     end)
   end
 
+  @spec count(tracker) :: pos_integer
+  def count(pid) do
+    pid
+    |> Agent.get(& &1)
+    |> Impl.count()
+  end
+
   @spec list_heartbeat_timestamps(tracker) :: [DateTime.t()]
   def list_heartbeat_timestamps(pid) do
     pid

fe_test_helpers/lib/fe_test_helpers/heartbeat_tracker/impl.ex

@@ -19,6 +19,11 @@ defmodule FETestHelpers.HeartbeatTracker.Impl do
     Enum.reverse(reversed_heartbeats)
   end
 
+  @spec count(t) :: non_neg_integer
+  def count(reversed_heartbeats) when is_impl(reversed_heartbeats) do
+    length(reversed_heartbeats)
+  end
+
   @spec list_heartbeat_intervals(t, System.time_unit()) :: [integer]
   def list_heartbeat_intervals(reversed_heartbeats, time_unit \\ :second) do
     reversed_heartbeats

fe_test_helpers/test/fe_test_helpers/heartbeat_tracker/impl_test.exs

@@ -13,6 +13,14 @@ defmodule FETestHelpers.HeartbeatTracker.ImplTest do
     assert DateTime.diff(recorded_timestamp, DateTime.utc_now(), :millisecond) < 20
   end
 
+  property "count/1 returns the number of recorded heartbeats" do
+    forall heartbeat_count <- non_neg_integer() do
+      impl = Impl.new() |> record_heartbeat_multiple_times(heartbeat_count)
+
+      heartbeat_count == Impl.count(impl)
+    end
+  end
+
   property "list_heartbeat_timestamps/1 returns the timestamps in the order received" do
     current_timestamp = DateTime.utc_now()
 

fe_test_helpers/test/fe_test_helpers/heartbeat_tracker_test.exs

@@ -4,18 +4,28 @@ defmodule FETestHelpers.HeartbeatTrackerTest do
 
   alias FETestHelpers.HeartbeatTracker
 
-  property "record_heartbeat/1 stores the heartbeat" do
-    forall [heartbeat_count <- non_neg_integer()] do
+  property "record_heartbeat/1 stores the current timestamp in order each time it's called" do
+    forall [heartbeat_count <- pos_integer()] do
       {:ok, tracker} = HeartbeatTracker.start_link([])
 
       record_heartbeat_multiple_times(tracker, heartbeat_count)
 
-      actual_heartbeat_count =
-        tracker
-        |> HeartbeatTracker.list_heartbeat_timestamps()
-        |> length()
+      timestamps = HeartbeatTracker.list_heartbeat_timestamps(tracker)
+
+      timestamps_sorted? =
+        Enum.sort_by(timestamps, &DateTime.to_unix(&1, :nanosecond)) == timestamps
+
+      timestamps_sorted?
+    end
+  end
+
+  property "count/1 returns the number of heartbeats recorded" do
+    forall [heartbeat_count <- non_neg_integer()] do
+      {:ok, tracker} = HeartbeatTracker.start_link([])
+
+      record_heartbeat_multiple_times(tracker, heartbeat_count)
 
-      actual_heartbeat_count == heartbeat_count
+      heartbeat_count == HeartbeatTracker.count(tracker)
     end
   end