Add test for race condition in community gardens

CONTRIBUTING.md

@@ -40,7 +40,7 @@ Please keep the following in mind:
 - Each problem should have a test suite, an example solution, and a template
   file for the real implementation. Read about [the anatomy of practice exercises](https://github.com/exercism/docs/blob/main/building/tracks/practice-exercises.md) or [the anatomy of concept exercises](https://github.com/exercism/docs/blob/main/building/tracks/concept-exercises.md), depending on to which type of exercise you want to contribute.
 
-- For practice exercises, `instructions.md` come from the [problem specifications](https://github.com/exercism/problem-specifications) repository. They cannot be changed without updating them in that repository first. If Elixir-specific changes are necessary, than can be appended to the instructions by creating a `instructions.append.md` file.
+- For practice exercises, `instructions.md` come from the [problem specifications](https://github.com/exercism/problem-specifications) repository. They cannot be changed without updating them in that repository first. If Elixir-specific changes are necessary, they can be appended to the instructions by creating a `instructions.append.md` file.
 
 - For practice exercises, use typespecs in the example and template files as described [here](https://elixir-lang.org/getting-started/typespecs-and-behaviours.html).
 

exercises/concept/community-garden/test/community_garden_test.exs

@@ -45,6 +45,32 @@ defmodule CommunityGardenTest do
     assert plot_3.plot_id == 3
   end
 
+  @tag task_id: 3
+  test "registered plots have incremental unique id when registered concurrently" do
+    {:ok, pid} = CommunityGarden.start()
+
+    total_plots = 20
+    test_process_pid = self()
+
+    Enum.each(1..total_plots, fn n ->
+      spawn(fn ->
+        plot = CommunityGarden.register(pid, "Mary Bumblebee #{n}")
+        send(test_process_pid, {n, plot})
+      end)
+    end)
+
+    plot_ids =
+      Enum.map(1..total_plots, fn n ->
+        receive do
+          {^n, plot} -> plot.plot_id
+        after
+          100 -> nil
+        end
+      end)
+
+    assert Enum.sort(plot_ids) == Enum.to_list(1..total_plots)
+  end
+
   @tag task_id: 4
   test "can release a plot" do
     assert {:ok, pid} = CommunityGarden.start()