Add specs for [Bug #20654] #1724

Job	Run time
RuboCop	28s
specs (ubuntu, 3.0.6)	1m 26s
specs (ubuntu, 3.1.4)	1m 33s
specs (ubuntu, 3.2.2)	1m 26s
specs (ubuntu, 3.3.0)	1m 24s
specs (macos, 3.0.6)	1m 21s
specs (macos, 3.1.4)	1m 17s
specs (macos, 3.2.2)	1m 9s
specs (macos, 3.3.0)	1m 7s
specs (windows, 3.0.6)	5m 39s
specs (windows, 3.1.4)	4m 44s
specs (windows, 3.2.2)	4m 5s
specs (windows, 3.3.0)	3m 59s
specs (ubuntu, 3.3.0, --enable-frozen-string-literal)	1m 24s
	31m 2s

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