Checking for tag names that include a colon

[codyrobbins]

We’re using Cloudflare’s ESI include functionality and in our Rails tests we’re trying to check for the presence of the ESI tags like so:

assert_select 'esi:include[src="/foo"]'

Unfortunately this doesn’t find the tag:

Expected at least 1 element matching "esi:include[src="/foo"]", found 0..
Expected 0 to be >= 1.

Every other attempt I’ve come up with to get this to work causes the wheels to fly off in one way or another:

assert_select 'esi\:include[src="/foo"]'
# Nokogiri::XML::XPath::SyntaxError: ERROR: Invalid expression: .//esi\:include[@src="/foo"] | self::esi\:include[@src="/foo"]

assert_select 'esi|include[src="/foo"]'
# Nokogiri::XML::XPath::SyntaxError: ERROR: Undefined namespace prefix: .//esi:include[@src="/foo"] | self::esi:include[@src="/foo"]

I also tried to pass multiple variations of an XPath selector directly using the local-name() function to no avail. Is there simply no way to check for the presence of a tag that includes a colon in its name with assert_select?