Do not crash on empty test unit groups, closes #14754

lib/ex_unit/lib/ex_unit/runner.ex

@@ -166,18 +166,23 @@ defmodule ExUnit.Runner do
     running
   end
 
-  defp spawn_modules(config, [{group, [_ | _] = modules} | groups], async?, running) do
-    if max_failures_reached?(config) do
-      running
-    else
-      {pid, ref} =
-        spawn_monitor(fn ->
-          Enum.each(modules, fn {module, params} ->
-            run_module(config, module, async?, group, params)
-          end)
-        end)
+  defp spawn_modules(config, [{group, modules} | groups], async?, running) do
+    cond do
+      max_failures_reached?(config) ->
+        running
 
-      spawn_modules(config, groups, async?, Map.put(running, ref, pid))
+      modules == [] ->
+        spawn_modules(config, groups, async?, running)
+
+      true ->
+        {pid, ref} =
+          spawn_monitor(fn ->
+            Enum.each(modules, fn {module, params} ->
+              run_module(config, module, async?, group, params)
+            end)
+          end)
+
+        spawn_modules(config, groups, async?, Map.put(running, ref, pid))
     end
   end
 

lib/ex_unit/test/ex_unit_test.exs

@@ -720,6 +720,30 @@ defmodule ExUnitTest do
     assert_receive {:tmp_dir, tmp_dir2} when tmp_dir1 != tmp_dir2
   end
 
+  test "empty parameterized tests" do
+    defmodule EmptyParameterizedTests do
+      use ExUnit.Case, async: true, parameterize: []
+
+      test "hello world" do
+        assert false
+      end
+    end
+
+    configure_and_reload_on_exit(trace: true)
+    assert capture_io(fn -> ExUnit.run() end) =~ "0 tests"
+
+    defmodule EmptyGroupedParameterizedTests do
+      use ExUnit.Case, async: true, parameterize: [], group: :example
+
+      test "hello world" do
+        assert false
+      end
+    end
+
+    configure_and_reload_on_exit(trace: true)
+    assert capture_io(fn -> ExUnit.run() end) =~ "0 tests"
+  end
+
   describe "after_suite/1" do
     test "executes all callbacks set in reverse order" do
       Process.register(self(), :after_suite_test_process)