diff --git a/lib/mix/lib/mix/tasks/test.ex b/lib/mix/lib/mix/tasks/test.ex
index 0e5fbb3f0b3..5f2bed5327e 100644
--- a/lib/mix/lib/mix/tasks/test.ex
+++ b/lib/mix/lib/mix/tasks/test.ex
@@ -430,6 +430,7 @@ defmodule Mix.Tasks.Test do
     elixir_version_check: :boolean,
     failed: :boolean,
     stale: :boolean,
+    repeat: :boolean,
     listen_on_stdin: :boolean,
     formatter: :keep,
     slowest: :integer,
@@ -573,6 +574,13 @@ defmodule Mix.Tasks.Test do
       warn_test_pattern
     )
 
+    # ExUnit.FailuresManifest.write(matched_test_files, ".mix_repeat_tests")
+
+    # matched_test_files |> IO.inspect(label: "test.ex:578: matched_test_files")
+    # test_paths |> IO.inspect(label: "test.ex:579: test_paths")
+    # test_elixirc_options |> IO.inspect(label: "test.ex:579: test_elixirc_options")
+    # opts |> IO.inspect(label: "test.ex:580: opts")
+
     case CT.require_and_run(matched_test_files, test_paths, test_elixirc_options, opts) do
       {:ok, %{excluded: excluded, failures: failures, total: total}} ->
         Mix.shell(shell)
@@ -746,6 +754,10 @@ defmodule Mix.Tasks.Test do
         Mix.raise("Combining --failed and --stale is not supported.")
       end
 
+      if opts[:repeat] do
+        Mix.raise("Combining --failed and --repeat is not supported.")
+      end
+
       {allowed_files, failed_ids} = ExUnit.Filters.failure_info(manifest_file)
       {Keyword.put(opts, :only_test_ids, failed_ids), allowed_files}
     else
diff --git a/lib/mix/test/mix/tasks/test_test.exs b/lib/mix/test/mix/tasks/test_test.exs
index b3b4a686401..ba52d98749d 100644
--- a/lib/mix/test/mix/tasks/test_test.exs
+++ b/lib/mix/test/mix/tasks/test_test.exs
@@ -60,6 +60,10 @@ defmodule Mix.Tasks.TestTest do
   describe "--stale" do
     test "runs all tests for first run, then none on second" do
       in_fixture("test_stale", fn ->
+        # mix(["test"])
+        # |> IO.inspect(label: "test_test.exs:64: mix test")
+        # |> tap(&IO.write(&1))
+
         assert_stale_run_output("2 tests, 0 failures")
 
         assert_stale_run_output("""