The members .nr and .alloc of an empty strvec are both zero and the
trailing NULL is provided by the shared global variable empty_strvec.
Once at least one item is added, .alloc needs to be bigger than .nr to
leave room for the terminating NULL.  The current .alloc check only
tests whether it's bigger or equal to .nr in all cases.

Tighten it depending on whether the strvec is backed by empty_strvec or
not.  A report for a non-zero .alloc in an empty strvec looks like this:

 # check "(&vec)->nr == (&vec)->alloc" failed at t/unit-tests/t-strvec.c:55
 #    left: 0
 #   right: 1

And .alloc being .equal to .nr in a non-empty strvec results in:

 # check "(&vec)->nr < (&vec)->alloc" failed at t/unit-tests/t-strvec.c:55
 #    left: 1
 #   right: 1

Signed-off-by: René Scharfe <redacted>
---
Bonus patch.

 t/unit-tests/t-strvec.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/t/unit-tests/t-strvec.c b/t/unit-tests/t-strvec.c
index fdb28ba220..6a4d425840 100644
--- a/t/unit-tests/t-strvec.c
+++ b/t/unit-tests/t-strvec.c

@@ -8,7 +8,9 @@
 		if (check_uint(ARRAY_SIZE(expect), >, 0) && \
 		    check_pointer_eq(expect[ARRAY_SIZE(expect) - 1], NULL) && \
 		    check_uint((vec)->nr, ==, ARRAY_SIZE(expect) - 1) && \
-		    check_uint((vec)->nr, <=, (vec)->alloc)) { \
+		    ((vec)->v == empty_strvec ? \
+		     check_uint((vec)->nr, ==, (vec)->alloc) : \
+		     check_uint((vec)->nr, <, (vec)->alloc))) { \
 			for (size_t i = 0; i < ARRAY_SIZE(expect); i++) { \
 				if (!check_str((vec)->v[i], expect[i])) { \
 					test_msg("      i: %"PRIuMAX, i); \
--

2.45.2