health insurance

Im afraid to test because i dont get health insurance till next month and even then i was told they could deny me if i test soon afterweards because they would say it was a preexisiting condition.im a temp where i work and when i get the insurance i will have to change to a different agency when im hired on.SO would that mean they wouldnt cover me?And if i ever lost this job would i just be screwed because whatever my next job is their insurance wouldnt cover me right.Sounds like im stuck where i work at i hoe thats not true though