Make test and test cases exit with reason :shutdown

This guarantees OTP processes are properly shutdown when
the test finishes.

Author: José Valim

lib/ex_unit/lib/ex_unit/callbacks.ex

@@ -23,7 +23,9 @@ defmodule ExUnit.Callbacks do
   Finally, `setup_all` callbacks run in the test case process, while all
   `setup` callbacks run in the same process as the test itself. `on_exit`
   callbacks always run in a separate process than the test case or the
-  test itself.
+  test itself. Since the test process exits with reason `:shutdown`, most
+  of times `on_exit/1` can be avoided as processes are going to clean
+  up on their own.
 
   ## Context
 

lib/ex_unit/lib/ex_unit/runner.ex

@@ -155,7 +155,7 @@ defmodule ExUnit.Runner do
             send parent, {self, :case_finished, test_case, failed_tests}
         end
 
-        receive do: ({^parent, :done} -> :done)
+        exit(:shutdown)
       end)
 
     {test_case, pending} =
@@ -167,9 +167,7 @@ defmodule ExUnit.Runner do
           {test_case, []}
       end
 
-    test_case = exec_on_exit(test_case, case_pid)
-    send case_pid, {parent, :done}
-    {test_case, pending}
+    {exec_on_exit(test_case, case_pid), pending}
   end
 
   defp exec_case_setup(%ExUnit.TestCase{name: case_name} = test_case) do
@@ -219,7 +217,7 @@ defmodule ExUnit.Runner do
           end)
 
         send parent, {self, :test_finished, %{test | time: us}}
-        receive do: ({^parent, :done} -> :done)
+        exit(:shutdown)
       end)
 
     test =
@@ -230,9 +228,7 @@ defmodule ExUnit.Runner do
           %{test | state: {:failed, {{:EXIT, test_pid}, error, []}}}
       end
 
-    test = exec_on_exit(test, test_pid)
-    send test_pid, {parent, :done}
-    test
+    exec_on_exit(test, test_pid)
   end
 
   defp exec_test_setup(%ExUnit.Test{case: case} = test, context) do

lib/ex_unit/test/ex_unit/callbacks_test.exs

@@ -105,18 +105,27 @@ defmodule ExUnit.CallbacksTest do
     on_exit fn -> ExUnit.configure(formatters: [ExUnit.CLIFormatter]) end
   end
 
-  test "kills test process only after on_exit runs" do
+  test "exits with shutdown reason" do
     defmodule OnExitAliveTest do
       use ExUnit.Case
 
       setup do
+        parent = self()
+
         pid = spawn_link fn ->
           Process.flag(:trap_exit, true)
-          receive do: ({:EXIT, _, _} -> :ok)
+          send parent, :ready
+          receive do
+            {:EXIT, ^parent, :shutdown} ->
+              receive do: ({:on_exit, pid} -> send pid, :done)
+          end
         end
 
+        receive do: (:ready -> :ok)
+
         on_exit fn ->
-          assert Process.alive?(pid)
+          send pid, {:on_exit, self}
+          assert_receive :done
           IO.puts "on_exit run"
         end