You need to be very careful when testing headphones: especially if you are carrying out the testing exercise prior to making a purchase decision.
Firstly, while testing headphones, you need to see how well the headphones perform at high (sound) volumes and at low volumes. It doesn’t matter whether the vendor claims that the headphones under consideration are the best earbuds or the best over ear headphones, it is still upon you to carry out the actual testing, in order to see how well they perform.
Secondly, while testing headphones, you need to see how well the headphones perform in terms of keeping unwanted sounds out. This is particularly important if, for instance, you are looking at best open over ear headphones. Granted, there are some specialized noise-cancelling headphones, but even those that are not specialized at this function should nonetheless have some basic noise cancellation capabilities.
Thirdly, while testing headphones, you need to see how comfortable the headphones are to wear. Again, granted, you don’t expect a pair of headphones to be as comfortable to wear as, say, as pair of Calvin Klein shorts, but the headphones should nonetheless be reasonable comfortable to wear. At the very least, you don’t want to end up with headphones that scratch your ears or otherwise cause injuries to you.