What does "publish" mean here? I thought "book" or "article" can be published, but how can the test be published?
You are correct. A "book" or an "article" can be published. "Published" means to prepare and print a written issue that will be available for sale or available to the public. Scientists don't only just publish tests. Scientists will publish their results, the hypothesis, the materials they used, etc. in a written document, such as an academic paper, to showcase the work they have done. These academic papers are usually printed and published in a scientific journal or on a scientific website.