With the release of the latest development preview most of the functions in the test libraries are marked as external, meaning they can be used for extension development!
Unfortunately the test toolkit is still a separate fob that has to be imported manually, however
if you’re using Docker together with the navcontainerhelper module you can import the fob automatically by adding the -includeTestToolkit switch parameter to the New-NavContainer cmdlet.
By default the AL: Download Symbols command will only download the ‘Application’ and ‘System’ symbol packages, but it’s also possible to download the ‘Test’ symbol package.
In the latest development preview (February) you can do this by specifying the “test” key in your app.json with the version of the test symbol package your extension depends on.
To retrieve the available symbol packages from your middle tier you can use the Get-NAVAppInfo -SymbolsOnly cmdlet in PowerShell and take the correct version number from there.
Now you can just use the ‘AL: Download Symbols’ command and it will also download the test symbol package!