Ynaig
Another test:
If the person you know might love her/himself then you can test the following way.
Look into her/his eyes for as long you can, don't worry about blinking. If you and her/him can maintain long gaze into each other's eyes, then both of you love themselves and each other.
If you can't maintain the long gaze, then you don't love yourself. If the other can't, then she/he does not love her/himself as well.
I also know that this test also works to determine if the person who tells the truth, the person won't break the gaze, but a liar always looks away from a long gaze.
Also it works for pets as well, with the only difference that the pets express the love unconditionally.
Ynaig