Infectious bronchitis can be hard to test for. It is a limited disease, lasting about a month, so it might be that it needs to be tested when symptoms are worst. IB virus can be responsible for many of the egg shell problems that we sometimes see. It also may be responsible for some hens having reproductive disorders. When my flock had IB going through it, most all eventually got it, and they sneezed every few minutes, but pretty much acted normal. I had to wait at least a year from the last sick bird before adding or hatching chicks, so as not to keep the disease from passing on. They can be carriers of IB for 5 months up to a year, depending on which source you read. I saw a couple of wrinkled egg shells, but later, many other shell problems. Here is a good article with examples of the many egg shell problems that IB can cause:
https://www.backyardchickens.com/articles/common-egg-quality-problems.65923/
https://www.backyardchickens.com/articles/common-egg-quality-problems.65923/