There is currently an issue in the package manager where `swift test` doesn't always build the most recent content in the repository. This is an artifact of the initial implementation, but it has one mildly useful feature which is that `swift test` will "happen" to build with the flags (-Xlinker, etc.) last passed to `swift build`. See:
I intend to fix this behavior, but please note that this will require everyone who currently needs to build with `-Xlinker ` etc. flags to pass them to *both* `swift build` and `swift test`.
I recognize this may be inconvenient in the short term, but it is more important that we fix `swift test` to always build the content present in the repository. The long term goal is, as ever, to provide explicit features instead of users needing to rely on the `-Xlinker` style flags.