Chemical Test revealed bad head gasket, but my car is showing no symptoms? Do you think it is ok or not?

my car- 2006 mk2 ford focus sport 1.8 TDCI
Bought it just over 12 months ago, it has already had about £1500 - £2, 000 on it in that time. The day I bought it, it was overheating on the way home and a garage said it was the head gasket, later found out it seems they lied and it was only the water pump and we paid them £900 ( well, Warrantywise did)

I notice a small drop of water of about 2 cups full per week and decided to get a chemical test done which changed colour almost right away and man said head gasket was gone.
There are no symptoms whatsoever, no power loss, no oil/water mixing, no smoke e.t.c.

Is it possible that there may have been old contaminants in the cooling system if the head gasket was actually replaced last time and why it is shown on the test?

I am looking at getting my timing belt replaced soon as I don't know for sure if they actually replaced it last year, if the head gasket needs doing then it makes sense to do it at same time so I need to be sure if has actually gone or not.

thanks

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