Define capture_subprocess_io from minitest

test/test_rake_file_utils.rb

@@ -342,6 +342,41 @@ def test_sh_if_a_command_exits_with_error_status_sh_echoes_it_fully
     end
   end
 
+  # https://github.com/seattlerb/minitest/blob/21d9e804b63c619f602f3f4ece6c71b48974707a/lib/minitest/assertions.rb#L188
+  def _synchronize
+    yield
+  end
+
+  # https://github.com/seattlerb/minitest/blob/21d9e804b63c619f602f3f4ece6c71b48974707a/lib/minitest/assertions.rb#L546
+  def capture_subprocess_io
+    _synchronize do
+      require "tempfile"
+
+      captured_stdout = Tempfile.new("out")
+      captured_stderr = Tempfile.new("err")
+
+      orig_stdout = $stdout.dup
+      orig_stderr = $stderr.dup
+      $stdout.reopen captured_stdout
+      $stderr.reopen captured_stderr
+
+      yield
+
+      $stdout.rewind
+      $stderr.rewind
+
+      return captured_stdout.read, captured_stderr.read
+    ensure
+      $stdout.reopen orig_stdout
+      $stderr.reopen orig_stderr
+
+      orig_stdout.close
+      orig_stderr.close
+      captured_stdout.close!
+      captured_stderr.close!
+    end
+  end
+
   def assert_echoes_fully
     long_string = "1234567890" * 10
     shell_command = "ruby -e\"'#{long_string}';exit false\""