test: Tweak JSON integer loading

Always load integers as unsigned and cast to the required type.
This will work for cases where a test case uses uint64 timestamps
while we use int64.

test/statetest/statetest_loader.cpp

@@ -33,13 +33,12 @@ static std::optional<T> integer_from_json(const json::json& j)
         return {};
 
     const auto s = j.get<std::string>();
-    size_t num_processed = 0;
-    T v = 0;
-    if constexpr (std::is_same_v<T, uint64_t>)
-        v = std::stoull(s, &num_processed, 0);
-    else
-        v = std::stoll(s, &num_processed, 0);
 
+    // Always load integers as unsigned and cast to the required type.
+    // This will work for cases where a test case uses uint64 timestamps while we use int64.
+    // TODO: Change timestamp type to uint64.
+    size_t num_processed = 0;
+    const auto v = static_cast<T>(std::stoull(s, &num_processed, 0));
     if (num_processed == 0 || num_processed != s.size())
         return {};
     return v;

test/unittests/statetest_loader_test.cpp

@@ -52,9 +52,16 @@ TEST(json_loader, int64_t)
         from_json<int64_t>(basic_json("9223372036854775807")), std::numeric_limits<int64_t>::max());
     EXPECT_EQ(from_json<int64_t>(basic_json("-9223372036854775808")),
         std::numeric_limits<int64_t>::min());
-    EXPECT_THROW(from_json<int64_t>(basic_json("0xffffffffffffffff")), std::out_of_range);
-    EXPECT_THROW(from_json<int64_t>(basic_json("9223372036854775808")), std::out_of_range);
-    EXPECT_THROW(from_json<int64_t>(basic_json("-9223372036854775809")), std::out_of_range);
+
+    // Unfortunate conversion results:
+    EXPECT_EQ(from_json<int64_t>(basic_json("0xffffffffffffffff")), int64_t{-1});
+    EXPECT_EQ(
+        from_json<int64_t>(basic_json("9223372036854775808")), std::numeric_limits<int64_t>::min());
+    EXPECT_EQ(from_json<int64_t>(basic_json("-9223372036854775809")),
+        std::numeric_limits<int64_t>::max());
+
+    EXPECT_THROW(from_json<uint64_t>(basic_json("0x10000000000000000")), std::out_of_range);
+    EXPECT_THROW(from_json<uint64_t>(basic_json("18446744073709551616")), std::out_of_range);
 
     // Octal is also supported.
     EXPECT_EQ(from_json<int64_t>(basic_json("0777")), 0777);