Captures all reported errors from within the block that match the given
error class.

reports = capture_reported_errors(IOError) do
    Rails.error.report(IOError.new("Oops"))
    Rails.error.report(IOError.new("Oh no"))
    Rails.error.report(StandardError.new)
end

assert_equal 2, reports.size
assert_equal "Oops", reports.first.error.message
assert_equal "Oh no", reports.last.error.message