So ends my excuse for not doing anything.

Follow Up: What is an Evaporation Line?
More than an hour after testing negative, as I was about to dispose of the test I saw that — gasp! — it showed a positive result. As I was certain that the test remained negative within the 10-15 minute time window, the change made me try another test from a different brand. The result was negative, and it has stayed negative after several hours.

So, what’s happening? Apparently, the test kit was neither defective nor showing a positive result. Most likely, it is showing an “evaporation line.” To confirm my status one way or the other, I will take another test tomorrow morning, as I was planning to do anyway.