Ensure ExUnit doesn't hang on linked failures

Thanks to @pminten for reporting this issue.

Author: José Valim

lib/ex_unit/lib/ex_unit/formatter.ex

@@ -131,6 +131,10 @@ defmodule ExUnit.Formatter do
     location_info("at #{location[:file]}:#{location[:line]}", color)
   end
 
+  defp format_stacktrace([], _case, _test, _color) do
+    ""
+  end
+
   defp format_stacktrace(stacktrace, _case, _test, color) do
     location_info("stacktrace:", color) <>
       Enum.map_join(stacktrace, fn(s) -> stacktrace_info format_stacktrace_entry(s), color end)

lib/ex_unit/lib/ex_unit/runner.ex

@@ -138,8 +138,8 @@ defmodule ExUnit.Runner do
     receive do
       { ^case_pid, :case_finished, test_case, tests } ->
         { test_case, tests }
-      { :DOWN, ^case_ref, :process, ^case_pid, { error, stacktrace } } ->
-        { test_case.state({ :failed, { :EXIT, error, prune_stacktrace(stacktrace) } }), [] }
+      { :DOWN, ^case_ref, :process, ^case_pid, error } ->
+        { test_case.state({ :failed, { :EXIT, error, [] } }), [] }
     end
   end
 
@@ -187,8 +187,8 @@ defmodule ExUnit.Runner do
     receive do
       { ^test_pid, :test_finished, test } ->
         test
-      { :DOWN, ^test_ref, :process, ^test_pid, { error, stacktrace } } ->
-        test.state { :failed, { :EXIT, error, prune_stacktrace(stacktrace) } }
+      { :DOWN, ^test_ref, :process, ^test_pid, error } ->
+        test.state { :failed, { :EXIT, error, [] } }
     end
   end
 

lib/ex_unit/test/ex_unit/formatter_test.exs

@@ -29,7 +29,6 @@ defmodule ExUnit.FormatterTest do
     assert format_test_failure(Hello, :world, failure, 1, nil) =~ """
       1) world (Hello)
          ** (RuntimeError) oops
-         stacktrace:
     """
   end
 
@@ -38,7 +37,6 @@ defmodule ExUnit.FormatterTest do
     assert format_test_failure(Hello, :world, failure, 1, nil) == """
       1) world (Hello)
          ** (exit) 1
-         stacktrace:
     """
   end
 
@@ -47,7 +45,6 @@ defmodule ExUnit.FormatterTest do
     assert format_test_failure(Hello, :world, failure, 1, nil) == """
       1) world (Hello)
          ** (throw) 1
-         stacktrace:
     """
   end
 
@@ -58,7 +55,6 @@ defmodule ExUnit.FormatterTest do
          ** (ExUnit.ExpectationError)
                       expected: 1
            to be equal to (==): 2
-         stacktrace:
     """
   end
 
@@ -70,7 +66,6 @@ defmodule ExUnit.FormatterTest do
               expected: ExUnit.FormatterTest.falsy()
                  to be: true
            instead got: false
-         stacktrace:
     """
   end
 
@@ -98,7 +93,6 @@ defmodule ExUnit.FormatterTest do
     assert format_test_case_failure(Hello, failure, 1, nil) =~ """
       1) Hello: failure on setup_all/teardown_all callback, tests invalidated
          ** (RuntimeError) oops
-         stacktrace:
     """
   end
 end

lib/ex_unit/test/ex_unit_test.exs

@@ -1,34 +1,6 @@
 Code.require_file "test_helper.exs", __DIR__
 
-defmodule ExUnit.NilFormatter do
-  @behaviour ExUnit.Formatter
-
-  def suite_started(_opts) do
-    :ok
-  end
-
-  def suite_finished(:ok, _run_us, _load_us) do
-    1
-  end
-
-  def case_started(:ok, _test_case) do
-    :ok
-  end
-
-  def case_finished(:ok, _test_case) do
-    :ok
-  end
-
-  def test_started(:ok, _test) do
-    :ok
-  end
-
-  def test_finished(:ok, _test) do
-    :ok
-  end
-end
-
-defmodule ExUnit.TestsCounterFormatter do
+defmodule ExUnit.CounterFormatter do
   @timeout 30_000
   @behaviour ExUnit.Formatter
 
@@ -79,9 +51,17 @@ end
 defmodule ExUnitTest do
   use ExUnit.Case, async: false
 
-  test "it supports many runs" do
-    ExUnit.configure(formatter: ExUnit.NilFormatter)
+  setup do
+    ExUnit.configure(formatter: ExUnit.CounterFormatter)
+    :ok
+  end
 
+  teardown do
+    ExUnit.configure(formatter: ExUnit.CLIFormatter)
+    :ok
+  end
+
+  test "it supports many runs" do
     defmodule SampleTest do
       use ExUnit.Case, async: false
 
@@ -94,12 +74,25 @@ defmodule ExUnitTest do
       end
     end
 
+    assert ExUnit.run == 2
+  end
+
+  test "it doesn't hang on exists" do
+    defmodule EventServerTest do
+      use ExUnit.Case, async: false
+
+      test "spawn and crash" do
+        Process.spawn_link(fn ->
+          exit :foo
+        end)
+        receive after: (1000 -> :ok)
+      end
+    end
+
     assert ExUnit.run == 1
   end
 
   test "filtering cases with tags" do
-    ExUnit.configure(formatter: ExUnit.TestsCounterFormatter)
-
     defmodule ParityTest do
       use ExUnit.Case