Cannot import XCTest in Playgrounds

I have just installed Playgrounds 3.3 and cannot import XCTest. I get the error "no such module 'XCTest'". Several tutorial sites imply that XCTest is built-in to Playgrounds and I have not found any other troubleshooting advice. I presume this must be some sort of configuration issue, but cannot identify anything.

Not sure it is relevant, but I have XCode 11.5 installed and the associated developer tools. Creating a playground in XCode allows me to import XCTest without any issues.

Any idea what would prevent me from import XCTest successfully?

Screenshot attached.