Your test file should be in a separate directory named Tests. Try running

swift package init --name MyPackage

inside a new empty directory. The generated files should demonstrate the expected structure of a basic package.

@hamishknight Could you transfer this please?

I think I'm getting close to it with https://github.com/jsumners/swift-experiments/tree/ebeb073deddda038183975caeea9c586eae1d633/json, but now I get an error about the Company type not being in scope.

Managed to trial and error into a working setup -- https://github.com/jsumners/swift-experiments/tree/57c28883c76aeed46151163c2d7dd68ffd461724/json

It would be very helpful if this were documented in a single place.

@AnthonyLatsis is correct swift package init is the fastest way to generate the minimal required structure of a package, with tests. There is also some more documentation available, though I think it could be improved to call out that tests are expected to live in the Tests folder.

It sounds like you've got something working now, so I'll close this issue out. If you have specific improvements or suggestions please feel free to open a new issue.

but now I get an error about the Company type not being in scope

Yeah, Company is not a module, so you cannot import it like that. You can either import the parent module like you already have, or use an import specifier like this: import struct Foo.Company. The module qualifier is always required. And we are not doing a great job at diagnosing this, but just import Foo is not enough as you see because Company is internal (the default access level).

I think what ended up making things work is @testable import Foo. Is that doing something to make Foo's symbols available to the external testing package?

Yes, basically, @testable gives access to internal stuff.

Thank you.