Include stracktrace on ExUnit timeouts

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

Author: José Valim

lib/ex_unit/lib/ex_unit/runner.ex

@@ -220,9 +220,17 @@ defmodule ExUnit.Runner do
           %{test | state: {:failed, {{:EXIT, test_pid}, error, []}}}
       after
         timeout ->
+          stacktrace =
+            try do
+              Process.info(test_pid, :current_stacktrace)
+            catch
+              _, _ -> []
+            else
+              {:current_stacktrace, stacktrace} -> stacktrace
+            end
           Process.exit(test_pid, :kill)
           Process.demonitor(test_ref, [:flush])
-          %{test | state: {:failed, {:error, %ExUnit.TimeoutError{timeout: timeout}, []}}}
+          %{test | state: {:failed, {:error, %ExUnit.TimeoutError{timeout: timeout}, stacktrace}}}
       end
 
     exec_on_exit(test, test_pid)

lib/ex_unit/test/ex_unit_test.exs

@@ -50,8 +50,9 @@ defmodule ExUnitTest do
       end
     end
 
-    assert capture_io(fn -> ExUnit.run end) =~
-           "** (ExUnit.TimeoutError) test timed out after 10ms"
+    output = capture_io(fn -> ExUnit.run end)
+    assert output =~ "** (ExUnit.TimeoutError) test timed out after 10ms"
+    assert output =~ ~r"\(stdlib\) timer\.erl:\d+: :timer\.sleep/1"
   end
 
   test "filtering cases with tags" do