Magento has several ways to match URLs. modules can register their own templates, and they will usually have the form / module / controller / action
In addition, CMS pages have URL identifiers, and they can be anything you like - they can contain / s to create the illusion of a hierarchy, but they are not significant.
Finally, categories and products have URL identifiers, and there is a whole table of rewriting URLs that map the path (/ [category] / [subcategory] / [product], for example) to the product. In your example, I would assume that the product URL identifier is "test123" and that the repository is configured for the URL suffix with ".html"
So, there is no file to view (in this case), but rather a database / administrator area.
source
share