test_diff_complicated.rb:8-11: Add tests for more...

[0pdd]

The puzzle 234-12f515de from #234 has to be resolved:

0pdd/test/test_diff_complicated.rb

Lines 8 to 11 in ca12334

	# @todo #234:15m Add tests for more complicated dynamics, like
	# [here](https://github.com/php-coder/mystamps/issues/695#issuecomment-405372820).
	# Ideally, this tests other cases that can lead to the observed behaviour,
	# but not covered by the test suite.

The puzzle was created by @yegor256 on 06-Oct-22.

Estimate: 15 minutes, role: DEV.

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