Could we get away with not putting the tests in libraries at all, and
instead having each SRFI's in a "123.scm" file that must be run as a
top-level program?

Then we can put `(import (srfi-test framework))` at the top of each such
file. The `(srfi-test framework)` library can re-export useful stuff
from the R7RS standard library, the R6RS standard library, or a Scheme
implementation's native library as needed. The most important procedures
for writing tests should work about equally no matter which of those
places they come from.

This approach would still be limited to Scheme implementations that
support `(import ...)` syntax, but that now covers almost all of the
main ones. Didn't Chicken 5 also switch from (use ...) to (import ...)
as its main library importing mechanism?