Improved test [skip ci]

Author: ankane

test/pqxx_test.cpp

@@ -1,3 +1,4 @@
+#include <limits>
 #include <optional>
 #include <string>
 #include <string_view>
@@ -324,6 +325,9 @@ void test_sparsevec_to_buf() {
     char buf[120];
     assert_equal(pqxx::to_buf(std::span<char>{buf}, pgvector::SparseVector{{1, 2, 3}}), "{1:1,2:2,3:3}/3");
 
+    int max = std::numeric_limits<int>::max();
+    assert_equal(pqxx::to_buf(std::span<char>{buf}, pgvector::SparseVector{{{max - 1, 1}}, max}), "{2147483647:1}/2147483647");
+
     assert_exception<pqxx::conversion_overrun>([] {
         return pqxx::to_buf(std::span<char>{}, pgvector::SparseVector{{1, 2, 3}});
     }, "Not enough space in buffer for sparsevec");