Suggestions for additional tests?

Some remarks on these tests:

1) In the example
   ${| print -v REPLY one word here; setopt shwordsplit }

Although the current context is used so the setopt persists after the
command is executed, the substitution code has already decided what
options apply to the result, so the words in this example are not
split.  It would be pretty complicated to invert that.

2) It occurred to me that ${|var| ...} is just another way to write
${${| ...}:-$var} (if REPLY remains unset).  So the former could be
dropped with no loss of functionality, if consensus deems it to be
fluff.

3) Note that ${|...} always substitutes at least an empty string, so
${${|...}-alt} is never "alt".

4) In the example
    print ${|return 1} $?
The value printed for $? is 1 but the status of the whole expression
is 0, that is, it is the status of the "print" command.

5) If a test sets the errreturn option, the whole test harness breaks
silently.  I encountered some other instances of that too, e.g., only
about half of the tests were run but the harness still reported "all
tests successful".

6) While writing the above I thought of another test I could add.  Later.