From 81a12973003757b22525f07afa72cfce9fdd2c3b Mon Sep 17 00:00:00 2001
From: Jason Axelson <jason.axelson@gmail.com>
Date: Sat, 12 Oct 2019 12:36:31 -0700
Subject: [PATCH] Add tests for file watcher

Also restructure Cortex.FileWatcher to better support testing
---
 lib/cortex/file_watcher.ex        | 39 ++++++++++++++++-----
 test/cortex/file_watcher_test.exs | 58 +++++++++++++++++++++++++++++++
 2 files changed, 88 insertions(+), 9 deletions(-)

diff --git a/lib/cortex/file_watcher.ex b/lib/cortex/file_watcher.ex
index 554cde0..2e7fb3d 100644
--- a/lib/cortex/file_watcher.ex
+++ b/lib/cortex/file_watcher.ex
@@ -8,30 +8,50 @@ defmodule Cortex.FileWatcher do
   use GenServer
 
   @watched_dirs ["lib/", "test/", "apps/"]
-  @throttle_timeout_ms 100
+  @default_throttle_timeout_ms 100
+  @default_file_changed_receiver Controller
 
   defmodule State do
-    defstruct [:watcher_pid, :file_events, :throttle_timer]
+    defstruct [
+      :watcher_pid,
+      :file_events,
+      :throttle_timer,
+      :throttle_timeout_ms,
+      :file_changed_receiver
+    ]
   end
 
   ##########################################
   # Public API
   ##########################################
 
-  def start_link do
-    GenServer.start_link(__MODULE__, [])
+  def start_link(opts \\ []) do
+    GenServer.start_link(__MODULE__, opts)
   end
 
   ##########################################
   # GenServer Callbacks
   ##########################################
 
-  def init(_) do
+  def init(opts) do
+    throttle_timeout_ms = Keyword.get(opts, :throttle_timeout_ms, @default_throttle_timeout_ms)
+
+    file_changed_receiver =
+      Keyword.get(opts, :file_changed_receiver, @default_file_changed_receiver)
+
     {:ok, watcher_pid} = FileSystem.start_link(dirs: watched_dirs())
 
     FileSystem.subscribe(watcher_pid)
 
-    {:ok, %State{watcher_pid: watcher_pid, throttle_timer: nil, file_events: %{}}}
+    initial_state = %State{
+      watcher_pid: watcher_pid,
+      throttle_timer: nil,
+      throttle_timeout_ms: throttle_timeout_ms,
+      file_changed_receiver: file_changed_receiver,
+      file_events: %{}
+    }
+
+    {:ok, initial_state}
   end
 
   def handle_info(
@@ -53,10 +73,10 @@ defmodule Cortex.FileWatcher do
   end
 
   def handle_info(:throttle_timer_complete, state) do
-    %State{file_events: file_events} = state
+    %State{file_events: file_events, file_changed_receiver: file_changed_receiver} = state
 
     Enum.each(file_events, fn {path, file_type} ->
-      GenServer.cast(Controller, {:file_changed, file_type, path})
+      GenServer.cast(file_changed_receiver, {:file_changed, file_type, path})
     end)
 
     {:noreply, %State{state | file_events: %{}, throttle_timer: nil}}
@@ -73,7 +93,8 @@ defmodule Cortex.FileWatcher do
   ##########################################
 
   defp maybe_update_throttle_timer(%State{throttle_timer: nil} = state) do
-    throttle_timer = Process.send_after(self(), :throttle_timer_complete, @throttle_timeout_ms)
+    %State{throttle_timeout_ms: throttle_timeout_ms} = state
+    throttle_timer = Process.send_after(self(), :throttle_timer_complete, throttle_timeout_ms)
     %State{state | throttle_timer: throttle_timer}
   end
 
diff --git a/test/cortex/file_watcher_test.exs b/test/cortex/file_watcher_test.exs
index 7da43e1..0ca8bc3 100644
--- a/test/cortex/file_watcher_test.exs
+++ b/test/cortex/file_watcher_test.exs
@@ -3,9 +3,67 @@ defmodule Cortex.FileWatcherTest do
 
   alias Cortex.FileWatcher
 
+  @throttle_timeout_ms 10
+
   test "file_type" do
     assert FileWatcher.file_type("test/some_file.exs") == :test
     assert FileWatcher.file_type("lib/some_file.ex") == :lib
     assert FileWatcher.file_type("lib/.#some_file.ex") == :unknown
   end
+
+  test "with one file event received, file changed is sent once" do
+    {watcher, watcher_pid} = start_file_watcher()
+
+    path = "test/some_file.exs"
+
+    send_file_event(watcher, watcher_pid, path, [:created, :modified])
+
+    assert_receive {:"$gen_cast", {:file_changed, :test, path}}
+    refute_receive {:"$gen_cast", {:file_changed, :lib, _}}
+  end
+
+  test "with one path event multiple times, file changed is sent once" do
+    {watcher, watcher_pid} = start_file_watcher()
+
+    path = "lib/some_file.ex"
+
+    send_file_event(watcher, watcher_pid, path, [:inodemetamod, :modified])
+    send_file_event(watcher, watcher_pid, path, [:inodemetamod, :modified])
+    send_file_event(watcher, watcher_pid, path, [:inodemetamod, :modified])
+
+    assert_receive {:"$gen_cast", {:file_changed, :lib, path}}
+    refute_receive {:"$gen_cast", {:file_changed, :lib, _}}
+  end
+
+  test "with multiple paths events sent multiple times, file changed is sent once per path" do
+    {watcher, watcher_pid} = start_file_watcher()
+
+    path1 = "lib/some_file.ex"
+    path2 = "lib/another_file.ex"
+
+    send_file_event(watcher, watcher_pid, path1, [:inodemetamod, :modified])
+    send_file_event(watcher, watcher_pid, path1, [:inodemetamod, :modified])
+    Process.sleep(3)
+    send_file_event(watcher, watcher_pid, path2, [:created, :modified])
+    send_file_event(watcher, watcher_pid, path1, [:inodemetamod, :modified])
+
+    assert_receive {:"$gen_cast", {:file_changed, :lib, path1}}
+    assert_receive {:"$gen_cast", {:file_changed, :lib, path2}}
+    refute_receive {:"$gen_cast", {:file_changed, :lib, _}}
+  end
+
+  defp start_file_watcher do
+    watcher =
+      start_supervised!(
+        {FileWatcher, file_changed_receiver: self(), throttle_timeout_ms: @throttle_timeout_ms}
+      )
+
+    %FileWatcher.State{watcher_pid: watcher_pid} = :sys.get_state(watcher)
+    {watcher, watcher_pid}
+  end
+
+  defp send_file_event(watcher, watcher_pid, path, events) do
+    message = {:file_event, watcher_pid, {path, events}}
+    send(watcher, message)
+  end
 end