ReSharper isn't displayed as "Installed" in Manage Extensions

Problem

After installing ReSharper, it still is not shown as "Installed" in the marketplace (Manage Extensions | Browse). Open "Manage Extensions" and search for "ReSharper". There is still the button "Install" next to it.

Question

Why is it so? How to understand if ReSharper is installed?

Resolution

This is by design. ReSharper is not a common vsix extension. There is no VSIX ID for the installed RS to map it to the Marketplace extension. One can verify if ReSharper is installed in the below way:

• Check the "Installed" tab in the "Manage Extensions" menu:
• Verify if there is a "ReSharper" item under the "Extensions |" menu item: