The standard backtrace filter for minitest.
See Minitest.backtrace_filter=.
Filter bt to something useful. Returns the whole thing if $DEBUG.
# File minitest-5.13.0/lib/minitest.rb, line 1013
def filter bt
return ["No backtrace"] unless bt
return bt.dup if $DEBUG
new_bt = bt.take_while { |line| line !~ MT_RE }
new_bt = bt.select { |line| line !~ MT_RE } if new_bt.empty?
new_bt = bt.dup if new_bt.empty?
new_bt
end