test(agent): clarify rnd usability smoke check

Reword the comment to state plainly that the real check is that calling the RNG on the
returned generator does not crash, and point to test_random.c:test_range for deterministic
seeding coverage. No behavior change.

Author: mfulb

axiom/tests/test_app.c

@@ -1256,8 +1256,13 @@ static void test_get_or_create_thread_rnd(void) {
   r1 = nr_app_get_or_create_thread_rnd(&app, 1);
   tlib_pass_if_not_null("first call returns non-NULL", r1);
 
-  /* Verify rnd is seeded and functional (not all-zero xsubi). */
-  tlib_pass_if_true("rnd produces in-range value",
+  /*
+   * The "< 1000" pulls little weight -- nr_random_range() is range-bounded for
+   * any seed, so it's near-tautological (would only trip if the range contract
+   * regressed). The real check here is that calling the RNG on the returned
+   * generator does not crash. Seeding is verified in test_random.c:test_range.
+   */
+  tlib_pass_if_true("rnd is usable (RNG call does not crash)",
                     nr_random_range(r1, 1000) < 1000,
                     "rnd=%p", (void*)r1);