The current COVID-19 test requirements for traveling to China consists of two PCR tests within 24 and 48 hours before departure respectively. In principle the rules can be different depending on the country you are traveling from, but this part seems to be the same for most countries. Another general rule seems to be that if you are transiting, you need to get tested and follow the instructions for both the country you start your trip in and in the last transit country before arriving in China.
Several countries seem to have special rules and processes for transiting passengers to make this practically possible (like relaxing the time requirements and having special testing providers that can guarantee two test results within the transfer time). Here is some information about procedures from Lufthansa, Finnair and the rules stated by the Chinese embassies in Germany and Finland that seem to confirm that this is possible.
I have a flight booked from Gothenburg, Sweden to Shanghai with a transit at Heathrow, and I am trying to find similar information for the UK, but reading the rules posted by the Chinese embassy in the UK, I can't find similar possibilities and no information about special testing procedures for transits to China at Heathrow. My flight is booked on a single ticket, but the first leg is operated by British Airways and the second by China Eastern, neither of which seem to have any online information pertaining to this. The transit time at Heathrow is only 4 hours and 25 minutes, while many other connections were only possible to book with 8-12 hours transit time (I'm beginning to see why). There are testing facilities at Heathrow that seem to be able to give results within 4 hours, but the UK rules doesn't seem to allow for two tests on the same day and my transit time would probably not be long enough to wait for both the test results and the "Green code" approval.
I am beginning to wonder if it is at all possible to fulfill the testing requirements with the itinerary I have booked (which makes me wonder why they would even sell me this ticket). I am wondering if anyone has experience transiting to China at Heathrow recently and how this worked out for them? Any other relevant information or suggestions would also be welcome.