t-reftable-pq: add tests for merged_iter_pqueue_top()

merged_iter_pqueue_top() as defined by reftable/pq.{c, h} returns
the element at the top of a priority-queue's heap without removing
it. Since there are no tests for this function in the existing
setup, add tests for the same.

Mentored-by: Patrick Steinhardt <ps@pks.im>
Mentored-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Chandra Pratap <chandrapratap3519@gmail.com>

t/unit-tests/t-reftable-pq.c

@@ -18,6 +18,11 @@ static void merged_iter_pqueue_check(const struct merged_iter_pqueue *pq)
 	}
 }
 
+static int pq_entry_equal(struct pq_entry *a, struct pq_entry *b)
+{
+	return !reftable_record_cmp(a->rec, b->rec) && (a->index == b->index);
+}
+
 static void t_pq_record(void)
 {
 	struct merged_iter_pqueue pq = { 0 };
@@ -42,9 +47,11 @@ static void t_pq_record(void)
 	} while (i != 1);
 
 	while (!merged_iter_pqueue_is_empty(pq)) {
+		struct pq_entry top = merged_iter_pqueue_top(pq);
 		struct pq_entry e = merged_iter_pqueue_remove(&pq);
 		merged_iter_pqueue_check(&pq);
 
+		check(pq_entry_equal(&top, &e));
 		check(reftable_record_type(e.rec) == BLOCK_TYPE_REF);
 		if (last)
 			check_int(strcmp(last, e.rec->u.ref.refname), <, 0);
@@ -82,9 +89,11 @@ static void t_pq_index(void)
 	while (i != 1);
 
 	for (i = N - 1; i > 0; i--) {
+		struct pq_entry top = merged_iter_pqueue_top(pq);
 		struct pq_entry e = merged_iter_pqueue_remove(&pq);
 		merged_iter_pqueue_check(&pq);
 
+		check(pq_entry_equal(&top, &e));
 		check(reftable_record_type(e.rec) == BLOCK_TYPE_REF);
 		check_int(e.index, ==, i);
 		if (last)
@@ -95,10 +104,51 @@ static void t_pq_index(void)
 	merged_iter_pqueue_release(&pq);
 }
 
+static void t_merged_iter_pqueue_top(void)
+{
+	struct merged_iter_pqueue pq = { 0 };
+	struct reftable_record recs[13];
+	size_t N = ARRAY_SIZE(recs), i;
+
+	for (i = 0; i < N; i++) {
+		reftable_record_init(&recs[i], BLOCK_TYPE_REF);
+		recs[i].u.ref.refname = (char *) "refs/heads/master";
+	}
+
+	i = 1;
+	do {
+		struct pq_entry e = {
+			.rec = &recs[i],
+			.index = i,
+		};
+
+		merged_iter_pqueue_add(&pq, &e);
+		merged_iter_pqueue_check(&pq);
+		i = (i * 7) % N;
+	}
+	while (i != 1);
+
+	for (i = N - 1; i > 0; i--) {
+		struct pq_entry top = merged_iter_pqueue_top(pq);
+		struct pq_entry e = merged_iter_pqueue_remove(&pq);
+
+		merged_iter_pqueue_check(&pq);
+		check(pq_entry_equal(&top, &e));
+		check(reftable_record_equal(top.rec, &recs[i], GIT_SHA1_RAWSZ));
+		for (size_t j = 0; i < pq.len; j++) {
+			check(pq_less(&top, &pq.heap[j]));
+			check_int(top.index, >, j);
+		}
+	}
+
+	merged_iter_pqueue_release(&pq);
+}
+
 int cmd_main(int argc, const char *argv[])
 {
 	TEST(t_pq_record(), "pq works with record-based comparison");
 	TEST(t_pq_index(), "pq works with index-based comparison");
+	TEST(t_merged_iter_pqueue_top(), "merged_iter_pqueue_top works");
 
 	return test_done();
 }