From 0ef6a316efb50a24dc4e4d688a28a91fa6363d5f Mon Sep 17 00:00:00 2001
From: Nelson Vides <nelson.vides@erlang-solutions.com>
Date: Sun, 22 Sep 2024 13:08:35 +0200
Subject: [PATCH] Add a test example of how to start a pool of supervisors

---
 test/echo_server.erl     |  5 +++++
 test/echo_supervisor.erl | 23 +++++++++++++++++++++++
 test/wpool_SUITE.erl     | 29 +++++++++++++++++++++++++++--
 3 files changed, 55 insertions(+), 2 deletions(-)
 create mode 100644 test/echo_supervisor.erl

diff --git a/test/echo_server.erl b/test/echo_server.erl
index 82d5012..d3b0d18 100644
--- a/test/echo_server.erl
+++ b/test/echo_server.erl
@@ -17,6 +17,7 @@
 -behaviour(gen_server).
 
 %% gen_server callbacks
+-export([start_link/1]).
 -export([init/1, terminate/2, code_change/3, handle_call/3, handle_cast/2, handle_info/2,
          handle_continue/2, format_status/1]).
 
@@ -26,6 +27,10 @@
 
 -export_type([from/0]).
 
+-spec start_link(term()) -> gen_server:start_ret().
+start_link(Something) ->
+    gen_server:start_link(?MODULE, Something, []).
+
 %%%===================================================================
 %%% callbacks
 %%%===================================================================
diff --git a/test/echo_supervisor.erl b/test/echo_supervisor.erl
new file mode 100644
index 0000000..66b3df7
--- /dev/null
+++ b/test/echo_supervisor.erl
@@ -0,0 +1,23 @@
+-module(echo_supervisor).
+
+-behaviour(supervisor).
+
+-export([start_link/0]).
+-export([init/1]).
+
+start_link() ->
+    supervisor:start_link({local, ?MODULE}, ?MODULE, noargs).
+
+init(noargs) ->
+    Children =
+        #{id => undefined,
+          start => {echo_server, start_link, []},
+          restart => transient,
+          shutdown => 5000,
+          type => worker,
+          modules => [echo_server]},
+    Strategy =
+        #{strategy => simple_one_for_one,
+          intensity => 5,
+          period => 60},
+    {ok, {Strategy, [Children]}}.
diff --git a/test/wpool_SUITE.erl b/test/wpool_SUITE.erl
index 07a1ae1..99ae2e3 100644
--- a/test/wpool_SUITE.erl
+++ b/test/wpool_SUITE.erl
@@ -28,7 +28,8 @@
 -export([stats/1, stop_pool/1, non_brutal_shutdown/1, brutal_worker_shutdown/1, overrun/1,
          kill_on_overrun/1, too_much_overrun/1, default_strategy/1, overrun_handler1/1,
          overrun_handler2/1, default_options/1, complete_coverage/1, child_spec/1, broadcall/1,
-         broadcast/1, send_request/1, worker_killed_stats/1, accepts_maps_and_lists_as_opts/1]).
+         broadcast/1, send_request/1, worker_killed_stats/1, accepts_maps_and_lists_as_opts/1,
+         pool_of_supervisors/1]).
 
 -elvis([{elvis_style, no_block_expressions, disable}]).
 
@@ -51,7 +52,8 @@ all() ->
      send_request,
      kill_on_overrun,
      worker_killed_stats,
-     accepts_maps_and_lists_as_opts].
+     accepts_maps_and_lists_as_opts,
+     pool_of_supervisors].
 
 -spec init_per_suite(config()) -> config().
 init_per_suite(Config) ->
@@ -515,6 +517,29 @@ accepts_maps_and_lists_as_opts(_Config) ->
 
     {comment, []}.
 
+-spec pool_of_supervisors(config()) -> {comment, string()}.
+pool_of_supervisors(_Config) ->
+    Opts =
+        #{workers => 3,
+          worker_shutdown => infinity,
+          worker => {supervisor, {echo_supervisor, echo_supervisor, noargs}}},
+
+    {ok, Pid} = wpool:start_sup_pool(pool_of_supervisors, Opts),
+    true = erlang:is_process_alive(Pid),
+
+    [begin
+         Run = fun(Sup) -> supervisor:start_child(Sup, [{ok, #{}}]) end,
+         {ok, EchoServer} = wpool:run(pool_of_supervisors, Run, next_worker),
+         true = erlang:is_process_alive(EchoServer)
+     end
+     || _N <- lists:seq(1, 9)],
+
+    Supervisors = wpool:get_workers(pool_of_supervisors),
+    [3 = proplists:get_value(active, supervisor:count_children(Supervisor))
+     || Supervisor <- Supervisors],
+
+    {comment, "Nicely load-balanced childrens across supervisors"}.
+
 %% =============================================================================
 %% Helpers
 %% =============================================================================