mix test --failed errors when failed tests are missing

lib/mix/lib/mix/tasks/test.ex

@@ -713,6 +713,16 @@ defmodule Mix.Tasks.Test do
               exit({:shutdown, 1})
             end)
 
+          total == 0 and opts[:failed] ->
+            message =
+              "\nERROR! Unable to find failed tests while using the --failed option"
+
+            IO.puts(:stderr, IO.ANSI.format([:red, message]))
+
+            System.at_exit(fn _ ->
+              exit({:shutdown, 1})
+            end)
+
           failures > 0 and opts[:raise] ->
             raise_with_shell(shell, "\"mix test\" failed")
 

lib/mix/test/fixtures/test_not_found/mix.exs

@@ -0,0 +1,11 @@
+defmodule TestFailed.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :test_not_found,
+      version: "0.0.1",
+      test_load_filters: [~r/.*_test_failed\.exs/]
+    ]
+  end
+end

lib/mix/test/fixtures/test_not_found/test/random_test_name_test_failed.exs

@@ -0,0 +1,6 @@
+defmodule OnlyFailingTest do
+  use ExUnit.Case
+
+  test "test number #{:random.uniform()} failed at #{DateTime.utc_now()}",
+    do: assert(System.get_env("PASS_FAILING_TESTS"))
+end

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

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

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

@@ -285,6 +285,21 @@ defmodule Mix.Tasks.TestTest do
         assert output =~ "** (RuntimeError) oops"
       end)
     end
+
+    test "fail with exit status 1 if failed tests cannot be found" do
+      in_fixture("test_not_found", fn ->
+        output = mix(["test", "--failed"])
+        assert output =~ "There are no tests to run"
+
+        # Run `mix test` once to record failures...
+        output = mix(["test"])
+        assert output =~ "1 test, 1 failure"
+
+        {output, exit_status} = mix_code(["test", "--failed"])
+        assert output =~ "ERROR! Unable to find failed tests while using the --failed option"
+        assert exit_status == 1
+      end)
+    end
   end
 
   describe "--listen-on-stdin" do