When you import tests from another site, the Release To information doesn't get cleared out and set to the current site. This prevents students from viewing the test if the test is published from the direct drop down "Publish" link.
1) Create 2 sites
2) 1st site: create a test with at least 1 question
3) 2nd site: import from 1st site (Site Info)
4) In dropdown, click publish and publish test
5) Become student in the 2nd site and notice the test doesn't show up