The new year has brought some much-needed hope to the Korean Peninsula, with Pyongyang and Seoul agreeing to talks next week about North Korea's participation in the upcoming Winter Olympics and reopening a long-dormant hotline for communication.

Meanwhile, in an apparent gesture of goodwill to the North, South Korea and the United States have also agreed to delay joint military exercises until after the Games.

But what concessions will North Korea make in return? So far, that remains unclear. Many analysts are watching for signs that Pyongyang is preparing to continue weapons testing despite the apparent detente with South Korea — a worrying possibility, given the rapid advances made by North Korea's weapons program in the past year.

“Further engine or flight tests in the near term would undermine Kim Jong Un’s own professed interest in talks with South Korea designed to reduce tensions, but I would not be surprised to see such weapons testing,” Daryl Kimball, executive director of the Arms Control Association, wrote in an email.

A weapons test in the next few weeks would add to North Korea's reputation as an unreliable negotiations partner. Even so, it may be difficult to know whether North Korea is preparing for one ahead of time — and in some cases, it may prove difficult to tell whether certain tests have taken place even after the fact.

On Tuesday, just after North Korea's Kim first raised the possibility of talks about the Olympics, CBS News reported that there had been activity at a location north of Pyongyang where a test of an intercontinental ballistic missile occurred in November. CBS national security correspondent David Martin reported that such a test could happen as early as this week.

Some analysts dismissed the possibility of an upcoming launch from the site identified by CBS. Jeffrey Lewis, director of the East Asia program at the James Martin Center for Nonproliferation Studies (CNS), suggested instead that the activity was related to Kim's claim during a New Year’s speech to “mass-produce nuclear warheads and ballistic missiles.”

Even without a test, that detail is not likely to reassure those scared of conflict — and there are other signs that North Korea's weapons development program may have tests on the way.

Over at 38 North, Joseph Bermudez, Frank Pabian and Jack Liu have analyzed commercial satellite imagery from late 2017 of a North Korean facility in Sohae. The analysts point to a number of signs — including the shift in the location of an environmental shelter that would have blocked the installation of test engines, as well as new construction — that raise the possibility that North Korea could be planning a missile engine test in the near future.

Importantly, this would be a new engine, rather than a new missile. The engine would not be used in a launch but instead would be run and monitored in a stationary position on a test stand, an operation to which the international community does not tend to respond.

38 North's analysts also caution that it is possible that a more innocuous logic may explain the movement at the site, including the testing of engines for a nonmilitary space-launch vehicle. In a phone call, Bermudez said that, in some cases, he thinks the North Koreans may deliberately move things at testing sites to confuse outside analysts. “They could be trying to manipulate us,” he said.

Still, many analysts have voiced concern that North Korea may try to develop a new solid-fuel engine for its missiles in 2018. Solid fuel can be stored in the engines, unlike more-volatile liquid fuel, and North Korea may be pursuing this technology to increase the maneuverability of its missile systems.

Shea Cotton, a CNS research associate, said that the Sohae facility had been used exclusively for liquid fuel tests and that it was not clear whether a solid-fuel engine could be tested at the location.

Either way, missile engine tests are fundamentally harder to track than flight tests or nuclear tests, both of which have big indicators for foreign powers to watch out for. Even with satellite imagery of the site, it can be difficult to confirm that an engine test has taken place. “Unless North Korea publicizes the tests, we might never hear about them,” Cotton said.

Though the international community has not typically condemned North Korea for engine tests or the manufacturing of missiles, in the context of the upcoming talks between North Korea and South Korea, such a development could cause problems. “While a rocket engine test would be less provocative than a flight test, it would still expose South Korean President Moon Jae-in to criticism that he is overeager to initiate dialogue with Pyongyang,” said Bruce Klingner, a former CIA analyst who is now the Heritage Foundation's top expert on North Korea.

Joel Wit, founder of the 38 North website and a former North Korea negotiator, said that the North Koreans “certainly understand that conducting a missile or nuclear test will create problems” but that actions such as engine tests fall in a “gray area” where the response would be hard to gauge.

Kimball also warned that North Korea would be more likely to conduct further weapons tests if the Trump administration were to send B-1B bombers or other military aircraft toward North Korea in the next few weeks. “Whether inter-Korean peace talks could continue if either side engages in what might be seen as a provocation would depend on the provocation,” Kimball said.

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