It seems that running ginkgo generate inside a go module, as per go 1.11, somewhere outside GOPATH results in a broken test skeleton.

Example:

package something_test

import (
	. "github.com/onsi/ginkgo"
	. "github.com/onsi/gomega"

	. "UNKNOWN_PACKAGE_PATH"
)

var _ = Describe("Something", func() {

})

The problem likely stems from the usage of ImportDir which does not work with go modules:

This has been described here:
golang/go#26504

A workaround is to use the golang.org/x/tools/go/packages package, however it is not stable yet.