Tests

Refactor pure text connection. #1373

Job	Run time
test (ruby=2.7)	39s
test (ruby=2.7, concurrency=async-websocket)	35s
test (ruby=3.0)	25s
test (ruby=3.1)	27s
test (ruby=3.2)	21s
test (ruby=3.3)	24s
test (ruby=ruby-head)	23s
test (ruby=jruby-head)	2m 5s
coveralls	5s
	5m 24s

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