Improve test relying on obscure test for duplicate verbose message

Author: MichaelChirico

inst/tests/tests.Rraw

@@ -14917,7 +14917,7 @@ test(2037.1, foo(DT), output='Please remember to always setDT()')
 # no assignment was made to DT
 test(2037.2, names(DT), 'a')
 # _selrefok() verbose message was duplicated
-test(2037.3, unname(table(unlist(strsplit(capture.output(foo(DT)), '\n|\\s+')))['ptr']), 1L)
+test(2037.3, foo(DT), output="data.table internal attributes", notOutput="data.table internal attributes.*data.table internal attributes")
 
 # `between` invalid args, and verbose #3516
 test(2038.01, between(1:5, 2, 4, incbounds=423), error="incbounds must be TRUE or FALSE")