XCTest の方は Swiftly を使っているならこれでサクッと再現できますね．

mkdir foo && cd foo echo main-snapshot-2025-10-16 > .swift-version swiftly install swift package init --type library --disable-swift-testing --enable-xctest swift sdk install https://download.swift.org/development/wasm-sdk/swift-DEVELOPMENT-SNAPSHOT-2025-10-16-a/swift-DEVELOPMENT-SNAPSHOT-2025-10-16-a_wasm.artifactbundle.tar.gz --checksum aa7251d0fbc44c0894335363f19e37a39dc323d3d8274ee8a7fe03b537c6cf67 swift build --build-tests --swift-sdk "$(swiftc -print-target-info | jq -r '.swiftCompilerTag')_wasm"

(edited)