Support :group option in ExUnit

lib/ex_unit/lib/ex_unit/case.ex

@@ -12,6 +12,11 @@ defmodule ExUnit.Case do
       It should be enabled only if tests do not change any global state.
       Defaults to `false`.
 
+    * `:group` - configures async tests in this module to run within a group.
+      Tests in the same group never run concurrently. Tests from different
+      groups can run concurrently with `async: true`.
+      Defaults to `nil`.
+
     * `:register` - when `false`, does not register this module within
       ExUnit server. This means the module won't run when ExUnit suite runs.
 
@@ -317,7 +322,7 @@ defmodule ExUnit.Case do
     end
 
     {register?, opts} = Keyword.pop(opts, :register, true)
-    {next_opts, opts} = Keyword.split(opts, [:async, :parameterize])
+    {next_opts, opts} = Keyword.split(opts, [:async, :group, :parameterize])
 
     if opts != [] do
       IO.warn("unknown options given to ExUnit.Case: #{inspect(opts)}")
@@ -552,6 +557,7 @@ defmodule ExUnit.Case do
 
     opts = Module.get_attribute(module, :ex_unit_module, [])
     async? = Keyword.get(opts, :async, false)
+    group = Keyword.get(opts, :group, nil)
     parameterize = Keyword.get(opts, :parameterize, nil)
 
     if not (parameterize == nil or (is_list(parameterize) and Enum.all?(parameterize, &is_map/1))) do
@@ -569,7 +575,11 @@ defmodule ExUnit.Case do
       end
 
       def __ex_unit__(:config) do
-        {unquote(async?), unquote(Macro.escape(parameterize))}
+        %{
+          async?: unquote(async?),
+          group: unquote(Macro.escape(group)),
+          parameterize: unquote(Macro.escape(parameterize))
+        }
       end
     end
   end

lib/ex_unit/lib/ex_unit/runner.ex

@@ -161,11 +161,22 @@ defmodule ExUnit.Runner do
     running
   end
 
-  defp spawn_modules(config, [{module, params} | modules], async?, running) do
+  defp spawn_modules(
+         config,
+         [{_group, group_modules} | modules],
+         async?,
+         running
+       ) do
     if max_failures_reached?(config) do
       running
     else
-      {pid, ref} = spawn_monitor(fn -> run_module(config, module, async?, params) end)
+      {pid, ref} =
+        spawn_monitor(fn ->
+          Enum.each(group_modules, fn {module, params} ->
+            run_module(config, module, async?, params)
+          end)
+        end)
+
       spawn_modules(config, modules, async?, Map.put(running, ref, pid))
     end
   end

lib/ex_unit/lib/ex_unit/server.ex

@@ -9,15 +9,21 @@ defmodule ExUnit.Server do
     GenServer.start_link(__MODULE__, :ok, name: @name)
   end
 
-  def add_module(name, {async?, parameterize}) do
+  def add_module(name, config) do
+    %{
+      async?: async?,
+      group: group,
+      parameterize: parameterize
+    } = config
+
     modules =
       if parameterize do
         Enum.map(parameterize, &{name, &1})
       else
         [{name, %{}}]
       end
 
-    case GenServer.call(@name, {:add, async?, modules}, @timeout) do
+    case GenServer.call(@name, {:add, {async?, group}, modules}, @timeout) do
       :ok ->
         :ok
 
@@ -51,6 +57,7 @@ defmodule ExUnit.Server do
     state = %{
       loaded: System.monotonic_time(),
       waiting: nil,
+      async_groups: %{},
       async_modules: :queue.new(),
       sync_modules: :queue.new()
     }
@@ -74,10 +81,20 @@ defmodule ExUnit.Server do
 
   # Called by the runner when --repeat-until-failure is used.
   def handle_call({:restore_modules, async_modules, sync_modules}, _from, state) do
+    {async_modules, async_groups} =
+      Enum.reduce(async_modules, {[], []}, fn
+        {nil, [module]}, {modules, groups} ->
+          {[{:module, module} | modules], groups}
+
+        {group, group_modules}, {modules, groups} ->
+          {[{:group, group} | modules], Map.put(groups, group, group_modules)}
+      end)
+
     {:reply, :ok,
      %{
        state
        | loaded: :done,
+         async_groups: async_groups,
          async_modules: :queue.from_list(async_modules),
          sync_modules: :queue.from_list(sync_modules)
      }}
@@ -91,7 +108,15 @@ defmodule ExUnit.Server do
       when is_integer(loaded) do
     state =
       if uniq? do
-        async_modules = :queue.to_list(state.async_modules) |> Enum.uniq() |> :queue.from_list()
+        async_modules =
+          state.async_modules
+          |> :queue.to_list()
+          |> Enum.uniq()
+          |> Enum.map(fn {group, modules} ->
+            {group, Enum.uniq(modules)}
+          end)
+          |> :queue.from_list()
+
         sync_modules = :queue.to_list(state.sync_modules) |> Enum.uniq() |> :queue.from_list()
 
         %{
@@ -107,26 +132,40 @@ defmodule ExUnit.Server do
     {:reply, diff, take_modules(%{state | loaded: :done})}
   end
 
-  def handle_call({:add, true, names}, _from, %{loaded: loaded} = state)
+  def handle_call({:add, {false = _async, _group}, names}, _from, %{loaded: loaded} = state)
+      when is_integer(loaded) do
+    state =
+      update_in(state.sync_modules, &Enum.reduce(names, &1, fn name, q -> :queue.in(name, q) end))
+
+    {:reply, :ok, state}
+  end
+
+  def handle_call({:add, {true = _async, nil = _group}, names}, _from, %{loaded: loaded} = state)
       when is_integer(loaded) do
     state =
       update_in(
         state.async_modules,
-        &Enum.reduce(names, &1, fn name, q -> :queue.in(name, q) end)
+        &Enum.reduce(names, &1, fn name, q -> :queue.in({:module, name}, q) end)
       )
 
-    {:reply, :ok, take_modules(state)}
+    {:reply, :ok, state}
   end
 
-  def handle_call({:add, false, names}, _from, %{loaded: loaded} = state)
+  def handle_call({:add, {true = _async, group}, names}, _from, %{loaded: loaded} = state)
       when is_integer(loaded) do
     state =
-      update_in(state.sync_modules, &Enum.reduce(names, &1, fn name, q -> :queue.in(name, q) end))
+      if Map.has_key?(state.async_groups, group) do
+        update_in(state.async_groups[group], &(names ++ &1))
+      else
+        state
+        |> put_in([:async_groups, group], names)
+        |> update_in([:async_modules], &:queue.in({:group, group}, &1))
+      end
 
     {:reply, :ok, state}
   end
 
-  def handle_call({:add, _async?, _names}, _from, state),
+  def handle_call({:add, {_async?, _group}, _names}, _from, state),
     do: {:reply, :already_running, state}
 
   defp take_modules(%{waiting: nil} = state) do
@@ -145,9 +184,26 @@ defmodule ExUnit.Server do
         state
 
       true ->
-        {modules, async_modules} = take_until(count, state.async_modules)
-        GenServer.reply(from, modules)
-        %{state | async_modules: async_modules, waiting: nil}
+        {async_modules, remaining_modules} = take_until(count, state.async_modules)
+
+        {async_modules, remaining_groups} =
+          Enum.reduce(async_modules, {[], state.async_groups}, fn
+            {:module, module}, {collected_modules, async_groups} ->
+              {[{nil, [module]} | collected_modules], async_groups}
+
+            {:group, group}, {collected_modules, async_groups} ->
+              {group_modules, async_groups} = Map.pop!(async_groups, group)
+              {[{group, group_modules} | collected_modules], async_groups}
+          end)
+
+        GenServer.reply(from, Enum.reverse(async_modules))
+
+        %{
+          state
+          | async_groups: remaining_groups,
+            async_modules: remaining_modules,
+            waiting: nil
+        }
     end
   end
 

lib/ex_unit/test/ex_unit_test.exs

@@ -715,6 +715,123 @@ defmodule ExUnitTest do
     assert_receive {:tmp_dir, tmp_dir2} when tmp_dir1 != tmp_dir2
   end
 
+  test "async tests run concurrently" do
+    Process.register(self(), :async_tests)
+
+    defmodule FirstAsyncTest do
+      use ExUnit.Case, async: true
+
+      test "first test" do
+        send(:async_tests, {:first_test, :started})
+        Process.sleep(10)
+        assert true
+        send(:async_tests, {:first_test, :finished})
+      end
+    end
+
+    defmodule SecondAsyncTest do
+      use ExUnit.Case, async: true
+
+      test "second test" do
+        send(:async_tests, {:second_test, :started})
+        Process.sleep(15)
+        assert true
+        send(:async_tests, {:second_test, :finished})
+      end
+    end
+
+    configure_and_reload_on_exit(max_cases: 2)
+
+    test_task =
+      Task.async(fn ->
+        capture_io(fn -> ExUnit.run() end)
+      end)
+
+    # Expected test distribution through time
+    #
+    # Time (ms): 0    10    20
+    #            |-----|-----|
+    # CPU0:      (  1  )
+    # CPU1:      (   2    )
+    assert_receive({:first_test, :started}, 5)
+    assert_receive({:second_test, :started}, 5)
+
+    # make sure we don't leave the task running after the outer test finishes
+    Task.await(test_task)
+  end
+
+  test "async tests run concurrently respecting groups" do
+    Process.register(self(), :async_grouped_tests)
+
+    defmodule RedOneTest do
+      use ExUnit.Case, async: true, group: :red
+
+      test "red one test" do
+        send(:async_grouped_tests, {:red_one, :started})
+        Process.sleep(30)
+        assert true
+        send(:async_grouped_tests, {:red_one, :finished})
+      end
+    end
+
+    defmodule RedTwoTest do
+      use ExUnit.Case, async: true, group: :red
+
+      test "red two test" do
+        send(:async_grouped_tests, {:red_two, :started})
+        Process.sleep(10)
+        assert true
+        send(:async_grouped_tests, {:red_two, :finished})
+      end
+    end
+
+    defmodule BlueOneTest do
+      use ExUnit.Case, async: true, group: :blue
+
+      test "blue one test" do
+        send(:async_grouped_tests, {:blue_one, :started})
+        Process.sleep(10)
+        assert true
+        send(:async_grouped_tests, {:blue_one, :finished})
+      end
+    end
+
+    defmodule BlueTwoTest do
+      use ExUnit.Case, async: true, group: :blue
+
+      test "blue two test" do
+        send(:async_grouped_tests, {:blue_two, :started})
+        Process.sleep(10)
+        assert true
+        send(:async_grouped_tests, {:blue_two, :finished})
+      end
+    end
+
+    configure_and_reload_on_exit(max_cases: 4)
+
+    test_task =
+      Task.async(fn ->
+        capture_io(fn -> ExUnit.run() end)
+      end)
+
+    # Expected test distribution through time
+    #
+    # Time (ms): 0    10    20    30    40
+    #            |-----|-----|-----|-----|
+    # CPU0:      (      R1         )( R2 )
+    # CPU1:      ( B1 )( B2 )
+    assert_receive({:red_one, :started}, 5)
+    assert_receive({:blue_one, :started}, 5)
+    refute_receive({:red_two, :started}, 25)
+    assert_received({:blue_one, :finished})
+    assert_received({:blue_two, :started})
+    assert_receive({:blue_two, :finished}, 15)
+    assert_receive({:red_two, :started}, 15)
+
+    # make sure we don't leave the task running after the outer test finishes
+    Task.await(test_task)
+  end
+
   describe "after_suite/1" do
     test "executes all callbacks set in reverse order" do
       Process.register(self(), :after_suite_test_process)
@@ -1101,6 +1218,54 @@ defmodule ExUnitTest do
     assert third =~ "ThirdTestFIFO"
   end
 
+  test "async test groups are run in compile order (FIFO)" do
+    defmodule RedOneFIFO do
+      use ExUnit.Case, async: true, group: :red
+
+      test "red one test" do
+        assert true
+      end
+    end
+
+    defmodule BlueOneFIFO do
+      use ExUnit.Case, async: true, group: :blue
+
+      test "blue one test" do
+        assert true
+      end
+    end
+
+    defmodule RedTwoFIFO do
+      use ExUnit.Case, async: true, group: :red
+
+      test "red two test" do
+        assert true
+      end
+    end
+
+    defmodule BlueTwoFIFO do
+      use ExUnit.Case, async: true, group: :blue
+
+      test "blue two test" do
+        assert true
+      end
+    end
+
+    configure_and_reload_on_exit(trace: true)
+
+    output =
+      capture_io(fn ->
+        assert ExUnit.run() == %{total: 4, failures: 0, excluded: 0, skipped: 0}
+      end)
+
+    [_, first, second, third, fourth | _] = String.split(output, "\n\n")
+
+    assert first =~ "RedOneFIFO"
+    assert second =~ "RedTwoFIFO"
+    assert third =~ "BlueOneFIFO"
+    assert fourth =~ "BlueTwoFIFO"
+  end
+
   test "can filter async tests" do
     defmodule FirstTestAsyncTrue do
       use ExUnit.Case, async: true