What does setting TEST_LOGS mean?

[Arthur Schwarz]

15.2.3 Parallel Test Harness

You can set the TEST_LOGS variable. By default, this variable is computed at
make run time from the value of TESTS as described above. For example, you
can use the following:

set x subset*.log; shift
env TEST_LOGS="foo.log $*" make -e check

What does setting TEST_LOGS do? It is read only in the Makefile file.

There is an unclear explanation of the TEST_LOGS meaning (don't explain, I
think I've got it figured out). And it sort of makes sense. TEST_LOGS
contains the name of all .log files. I get that. What happens if the user
changes one or all the names. Suppose Makefile looks something like:

   TESTS = foo.exe

Then
   TEST_LOGS = foo.log

And the user sets this to
   env TEST_LOGS = bar.log make -e check

What on earth does this mean?

And the examples with TEST_EXTENSIONS and duplicate base names (test cases
with extensions removed, like TESTS = test.sh test.pl and TEST_EXTENSIONS =
.pl .sh) grows even more complex.

Any idea?

And what does 'set x subset*.log; shift' have to do with anything. It looks
like something erroneously removed from an existing script and put in the
document.