Can your health insurance decline you if you get diagnosed right after coverage starts?

For the last few weeks I have been having some symptoms that are worrying me. I signed up and was approved for health insurance through Cigna and coverage starts next week. I plan to go in and get some tests done like blood test, ct scan and MRI. I figure that as long as I don't make an appointment until after coverage starts than I am ok. Am I correct? BTW, I have never been diagnosed with anything related.