go test regex type or syntax

What type or syntax of regex is used when running go test -r <regex> commands? I'm using -list to find the tests I want to run before using -r, like this:

go test -list 'Foo' *.go

I'm having specific difficulty with the following two test names:

func TestSendTrap(...
func TestSendTrapFull(...

This works:

go test -list 'TestSendTrap\b' *.go

So I'm presuming PCRE syntax is being used, but command go doesn't detail.