In a similar situation, with no paperwork issued albeit a short "started consumption test xxxxkm, to return at xxxxkm" and filler cap and dipstick was not stuck over to prevent tampering because "we trust you not to do anything with it"..

Been back for 4-5 times now and still the usual "keep filling it up because this is ongoing..." - only up till the last time I was in for a fill and the clutch replacement they stuck a big "HOLD" sticker over it.

Now the light's back on and will probably need to pop in sometime tomorrow... flicked an email through.

Would be a miracle if they start being specific about what my car's going through on the tests