In case anybody accidentally uses = for assignment instead of <- in a testthat tests file, currently this error comes up in the GitHub version of the package:
Error in doc_parse_raw(x, encoding = encoding, base_url = base_url, as_html = as_html, :
Opening and ending tag mismatch: expr line 8 and equal_assign [76]
Calls: lint_package ... read_xml.character -> read_xml.raw -> doc_parse_raw