random failures in GitHub Actions CI's macos

Start with the failing GitHub Actions run and gems/src/debug/test/debug/debug_statement_test.rb, especially test_breakpoint_fires_correctly and the support helpers named in the trace. Reproduce the bundled-gems test on macOS and determine why the expected Foo#bar output is intermittent; done means the test passes reliably in the macOS CI job.

debug gem sometimes failed on test-bundled-gems.

recent failures:
https://github.com/ruby/actions/runs/5515459899?check_suite_focus=true#step:16:2055

Testing the debug gem
  creating Makefile
  compiling /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/ext/debug/debug.c
  compiling /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/ext/debug/iseq_collector.c
  linking shared-object debug/debug.bundle
  /Users/runner/work/actions/actions/snapshot-master/exe/ruby -C /Users/runner/work/actions/actions/snapshot-master/gems/src/debug -Ilib /Users/runner/work/actions/actions/snapshot-master/.bundle/bin/rake test
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/lib/debug/client.rb:178: warning: assigned but unused variable - e
  Tests on local and remote. You can disable remote tests with RUBY_DEBUG_TEST_NO_REMOTE=1.
  Loaded suite /Users/runner/work/actions/actions/snapshot-master/.bundle/gems/rake-13.0.6/lib/rake/rake_test_loader
  Started
  ....................................P
  ===============================================================================
  Pending: test_boot_configuration_works_correctly(DEBUGGER__::BootConfigTest1638611290): Tests for DAP were skipped. You can enable them with RUBY_DEBUG_DAP_TEST=1.
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/dap_utils.rb:168:in `run_dap_scenario'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/dap/boot_config_test.rb:21:in `test_boot_configuration_works_correctly'
       18:     RUBY
       19:     
       20:     def test_boot_configuration_works_correctly
    => 21:       run_dap_scenario PROGRAM do
       22:         [
       23:           *INITIALIZE_MSG,
       24:           {
  ===============================================================================
  ..............................P
  ===============================================================================
  Pending: test_break_works_correctly(DEBUGGER__::BreakTest1638674577): Tests for DAP were skipped. You can enable them with RUBY_DEBUG_DAP_TEST=1.
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/dap_utils.rb:168:in `run_dap_scenario'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/dap/break_test.rb:21:in `test_break_works_correctly'
       18:     RUBY
       19:     
       20:     def test_break_works_correctly
    => 21:       run_dap_scenario PROGRAM do
       22:         [
       23:           *INITIALIZE_MSG,
       24:           {
  ===============================================================================
  ..............................F
  ===============================================================================
  Failure: test_breakpoint_fires_correctly(DEBUGGER__::BasicTest):
    #<Test::Unit::AssertionFailedError: 
    --------------------
    | Debugger Session |
    --------------------
    
    > 
    > Stop by SIGURG
    > continue
    > [?2004h(rdbg:remote) continue
    > [?2004l
  [1, 7] in /var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/debug-20220311-84898-50pfy5.rb
    > =>   1| class Foo
    >      2|   def bar
    >      3|     binding.break
    >      4|   end
    >      5| end
    >      6| 
    >      7| Foo.new.bar
    > =>#0	<main> at /var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/debug-20220311-84898-50pfy5.rb:1
    
    
    --------------------
    | Debuggee Session |
    --------------------
    
    > EBUGGER: Debugger can attach via UNIX domain socket (/var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/ruby-debug-sock-501/ruby-debug-runner-84898-86)
    > DEBUGGER: Connected.
    
    
    -------------------
    | Failure Message |
    -------------------
    
    Expected to include `"Foo\\#bar"` in
    (
    [?2004h(rdbg:remote) continue
    [?2004l
  [1, 7] in /var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/debug-20220311-84898-50pfy5.rb
    =>   1| class Foo
         2|   def bar
         3|     binding.break
         4|   end
         5| end
         6| 
         7| Foo.new.bar
    =>#0	<main> at /var/folders/24/8k48jl6d249_n_qfxwsl6xvm0000gn/T/debug-20220311-84898-50pfy5.rb:1
    )
     on UNIX Domain Socket mode.>.
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/assertions.rb:79:in `assert_block'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/utils.rb:78:in `rescue in block in debug_code'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/utils.rb:63:in `block in debug_code'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/utils.rb:171:in `prepare_test_environment'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/utils.rb:61:in `debug_code'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/debug/debug_statement_test.rb:12:in `block in debug_code'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/debug/debug_statement_test.rb:11:in `each'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/debug/debug_statement_test.rb:11:in `debug_code'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/debug/debug_statement_test.rb:31:in `test_breakpoint_fires_correctly'
       28:     end
       29: 
       30:     def test_breakpoint_fires_correctly
    => 31:       debug_code(program) do
       32:         type 'continue'
       33:         assert_line_text('Foo#bar')
       34:         type 'q!'
  ===============================================================================
  .................P
  ===============================================================================
  Pending: test_1639[2181](https://github.com/ruby/actions/runs/5515459899?check_suite_focus=true#step:16:2181)22(DEBUGGER__::DetachTest1639218122): Tests for DAP were skipped. You can enable them with RUBY_DEBUG_DAP_TEST=1.
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/dap_utils.rb:168:in `run_dap_scenario'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/dap/detach_test.rb:24:in `test_1639218122'
       21:     RUBY
       22:     
       23:     def test_1639218122
    => 24:       run_dap_scenario PROGRAM do
       25:         [
       26:           *INITIALIZE_MSG,
       27:           {
  ===============================================================================
  .................P
  ===============================================================================
  Pending: test_finish_works_correctly(DEBUGGER__::FinishTest1638674323): Tests for DAP were skipped. You can enable them with RUBY_DEBUG_DAP_TEST=1.
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/dap_utils.rb:168:in `run_dap_scenario'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/dap/finish_test.rb:21:in `test_finish_works_correctly'
       18:     RUBY
       19:     
       20:     def test_finish_works_correctly
    => 21:       run_dap_scenario PROGRAM do
       22:         [
       23:           *INITIALIZE_MSG,
       24:           {
  ===============================================================================
  .......P
  ===============================================================================
  Pending: test_hover_works_correctly(DEBUGGER__::HoverTest1638791703): Tests for DAP were skipped. You can enable them with RUBY_DEBUG_DAP_TEST=1.
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/dap_utils.rb:168:in `run_dap_scenario'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/dap/hover_test.rb:17:in `test_hover_works_correctly'
       14:     RUBY
       15:     
       16:     def test_hover_works_correctly
    => 17:       run_dap_scenario PROGRAM do
       18:         [
       19:           *INITIALIZE_MSG,
       20:           {
  ===============================================================================
  ....................P
  ===============================================================================
  Pending: test_next_works_correctly(DEBUGGER__::NextTest1638676688): Tests for DAP were skipped. You can enable them with RUBY_DEBUG_DAP_TEST=1.
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/dap_utils.rb:168:in `run_dap_scenario'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/dap/next_test.rb:21:in `test_next_works_correctly'
       18:     RUBY
       19:     
       20:     def test_next_works_correctly
    => 21:       run_dap_scenario PROGRAM do
       22:         [
       23:           *INITIALIZE_MSG,
       24:           {
  ===============================================================================
  ........................................P
  ===============================================================================
  Pending: test_step_back_works_correctly(DEBUGGER__::StepBackTest1638698086): Tests for DAP were skipped. You can enable them with RUBY_DEBUG_DAP_TEST=1.
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/dap_utils.rb:168:in `run_dap_scenario'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/dap/step_back_test.rb:23:in `test_step_back_works_correctly'
       20:     RUBY
       21:     
       22:     def test_step_back_works_correctly
    => 23:       run_dap_scenario PROGRAM do
       24:         [
       25:           *INITIALIZE_MSG,
       26:           {
  ===============================================================================
  P
  ===============================================================================
  Pending: test_step_works_correctly(DEBUGGER__::StepTest1638676609): Tests for DAP were skipped. You can enable them with RUBY_DEBUG_DAP_TEST=1.
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/support/dap_utils.rb:168:in `run_dap_scenario'
  /Users/runner/work/actions/actions/snapshot-master/gems/src/debug/test/dap/step_test.rb:21:in `test_step_works_correctly'
       18:     RUBY
       19:     
       20:     def test_step_works_correctly
    => 21:       run_dap_scenario PROGRAM do
       22:         [
       23:           *INITIALIZE_MSG,
       24:           {
  ===============================================================================
  ........................
  Finished in 138.555133 seconds.
  -------------------------------------------------------------------------------
  230 tests, 351 assertions, 1 failures, 0 errors, 8 pendings, 0 omissions, 0 notifications
  96.087% passed
  -------------------------------------------------------------------------------
  1.66 tests/s, 2.53 assertions/s
  rake aborted!
  Command failed with status (1)
  /Users/runner/work/actions/actions/snapshot-master/.bundle/gems/rake-13.0.6/exe/rake:27:in `<top (required)>'
  Tasks: TOP => test
  (See full trace by running task with --trace)
  Tests failed with exit code 1
Failed gems: debug
make: *** [test-bundled-gems-run] Error 1
Error: Process completed with exit code 2.