RuboCop requires using Utils.safe_popen_read and Utils.safe_popen_write
instead of Utils.popen_read and Utils.popen_write respectively.
Using the "safe" version means that an error will be shown if the
command fails. Previously, when using `popen_read`, a failed command can
go unnoticed and have negative consequences that go undetected (as
happened for pipend in
https://github.com/Homebrew/homebrew-core/pull/55682)
RuboCop does not require Utils.safe_popen_read in a test do block
because there can be some legitimate uses for Utils.popen_read in these
cases.
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