Fix mix test --only async:true/false

lib/ex_unit/lib/ex_unit/case.ex

@@ -624,6 +624,7 @@ defmodule ExUnit.Case do
 
     moduletag = Module.get_attribute(mod, :moduletag)
     tag = Module.delete_attribute(mod, :tag)
+    {async, _parameterize} = Module.get_attribute(mod, :ex_unit_module)
 
     {name, describe, describe_line, describetag} =
       case Module.get_attribute(mod, :ex_unit_describe) do
@@ -648,6 +649,7 @@ defmodule ExUnit.Case do
         line: line,
         file: file,
         registered: registered,
+        async: async,
         describe: describe,
         describe_line: describe_line,
         test_type: test_type

lib/mix/test/fixtures/test_async/lib/a.ex

@@ -0,0 +1,3 @@
+defmodule A do
+  def f, do: :ok
+end

lib/mix/test/fixtures/test_async/lib/b.ex

@@ -0,0 +1,3 @@
+defmodule B do
+  def f, do: A.f()
+end

lib/mix/test/fixtures/test_async/mix.exs

@@ -0,0 +1,11 @@
+defmodule TestAsync.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :test_async,
+      version: "0.0.1",
+      test_pattern: "*_test_async.exs"
+    ]
+  end
+end

lib/mix/test/fixtures/test_async/test/a_test_async.exs

@@ -0,0 +1,7 @@
+defmodule ATest do
+  use ExUnit.Case, async: true
+
+  test "f async" do
+    assert A.f() == :ok
+  end
+end

lib/mix/test/fixtures/test_async/test/b_test_async.exs

@@ -0,0 +1,7 @@
+defmodule BTest do
+  use ExUnit.Case, async: false
+
+  test "f sync" do
+    assert B.f() == :ok
+  end
+end

lib/mix/test/fixtures/test_async/test/test_helper.exs

@@ -0,0 +1 @@
+ExUnit.start()

lib/mix/test/mix/tasks/test_test.exs

@@ -620,6 +620,26 @@ defmodule Mix.Tasks.TestTest do
     end
   end
 
+  describe "--only" do
+    test "runs only async tests with --only async:true" do
+      in_fixture("test_async", fn ->
+        output = mix(["test", "--only", "async:true", "--trace"])
+        assert output =~ "2 tests, 0 failures, 1 excluded"
+        assert output =~ ~r/test f async \(.*ms\)/
+        assert output =~ "test f sync (excluded)"
+      end)
+    end
+
+    test "runs only sync tests with --only async:false" do
+      in_fixture("test_async", fn ->
+        output = mix(["test", "--only", "async:false", "--trace"])
+        assert output =~ "2 tests, 0 failures, 1 excluded"
+        assert output =~ ~r/test f sync \(.*ms\)/
+        assert output =~ "test f async (excluded)"
+      end)
+    end
+  end
+
   defp receive_until_match(port, expected, acc) do
     receive do
       {^port, {:data, output}} ->