In our Gemeinde and the ones of a few friends, the firm who does the mandatory sweeping of the chimney comes round on a different day of the year in the same van, but with a different person, to make the emissions testing.
I asked both why they did not do it at the same time and was told the rehearsed reply that "they were not qualified to do each others job".
Real high tech stuff cleaning chimneys on oil heaters - I don't think. The gas test is also an automatic machine which must take a maximum of a week's training.
Totally dodgy as I later discovered from my Stamm Tische "friends". These firms work as local cartels and have their own areas of control. By mutual agreement, they will refuse to work in each others areas. They come round twice so they can get twice as much dosh from you. Chances are that whoever does your neighbours emissions test is the only one you will ever find to come into your home.
Normally they post a card once a year each
for the cleaning and testing and TELL YOU when they are coming. If you ring up the number of the boiler maintainer, chances are he will come and test your emissions, but this will not count as the "official" yearly or two yearly test. In other Gemeindes apparently the emissions test is every two years.
In my case, the heater installer seems to have done half of the village and his family and the Kaminfegers have been close for generations. Also I am convinced that some of the Gemeinde folk get nice backhanders and free service. (Sorry I am a cynic).
Unless you are worried about carbon monoxide or strange smells, I would be tempted to wait for your appointment. Otherwise, my first stop would be to ask the neighbour or go to the Gemeinde or commune. (all records will be held there anyway). I am not sure how expensive canaries are, but this is an old miners emission test you could try while waiting for the letter.
If you have young kids, I would suggest a career in this line of work - job for life with good money.
I was thinking of asking someone from Germany to come round and do the cleaning and testing and submit the results to the Gemeinde (to see what happens) - I reckon that the local cartel would probably let his tyres down