Run all available tests if there are no pending --failed tests

Closes #10781

Author: josevalim

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

@@ -116,7 +116,8 @@ defmodule Mix.Tasks.Test do
     * `--export-coverage` - the name of the file to export coverage results to.
       Only has an effect when used with `--cover`
 
-    * `--failed` - runs only tests that failed the last time they ran
+    * `--failed` - runs only tests that failed the last time they ran.
+      If there are no pending --failed tests, `mix test` will run all available tests
 
     * `--force` - forces compilation regardless of modification times
 
@@ -688,7 +689,13 @@ defmodule Mix.Tasks.Test do
       end
 
       {allowed_files, failed_ids} = ExUnit.Filters.failure_info(manifest_file)
-      {Keyword.put(opts, :only_test_ids, failed_ids), allowed_files}
+
+      if MapSet.size(failed_ids) == 0 do
+        Mix.shell().info("No pending --failed tests, re-running all available tests...")
+        {opts, nil}
+      else
+        {Keyword.put(opts, :only_test_ids, failed_ids), allowed_files}
+      end
     else
       {opts, nil}
     end

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

@@ -215,7 +215,9 @@ defmodule Mix.Tasks.TestTest do
         assert mix(["test", "--failed"]) =~ "2 tests, 0 failures"
 
         # Nothing should get run if we try it again since everything is passing.
-        assert mix(["test", "--failed"]) =~ "There are no tests to run"
+        output = mix(["test", "--failed"])
+        assert output =~ "No pending --failed tests, re-running all available tests..."
+        assert output =~ "4 tests, 0 failures"
 
         # `--failed` and `--stale` cannot be combined
         output = mix(["test", "--failed", "--stale"])