Reality testing is the process of checking your internal thoughts against external reality. It is taught to patients in psychotherapy as a way to escape from excessively negative thought patterns. For example, someone is rude to you and you think, "People are always being rude to me." Reality testing would be actually thinking about all of the interactions you have with people and estimating how often people are rude. Always is likely not the answer.
Grenadline does something that hurts Cosma. Cosma assumes the Grendaline did it with the purpose of hurting Cosma. Cosma is encouraged to think about the events, consider possible motives other than malice, and, depending on the relationship, maybe even ask Grendaline why.
A couple of years ago I took Cognitive Behavioural Therapy. It was a group thing. In one class the instructor talked about this idea of reality testing, and in one case used an example like that one: an example where the way to test reality was to ask someone what they thought.
Well, this didn't sound right to me at all. Asking people how they feel or what they think is certainly a tool you can use to figure out how they feel or what they think, but it doesn't give certain results, it isn't superior to all other tools, and I don't even think it's a very potent tool.
We started to discuss that and after I'd wasted about ten minutes of the group's time someone asked if we could move on and we had a unanimous decision to do so. Still, to me the idea that asking someone how they feel is the definitive or even the best way to know how they feel isn't very well reality tested itself.
I have a toddler. I can certainly ask her how she feels, and sometimes I think she gets it right, but generally I'm as good or better at identifying her emotions. Of course, that's a toddler, what about adults? The question - and this is a really useful kind of question - is at what age a person might be presumed to stop being a deluded liar. I've known people of nearly every age there is for human being to be and I feel like I can say confidently that there is no magical day when being wrong about your own state is replaced being right about your own state. Instead, there is talent and practice, just like everything else.
But there is also talent and practice when it comes to judging the feelings of other people. Maybe you are great at understanding your own emotions, but that doesn't mean someone else isn't better. Maybe you are really bad at surmising other people's emotions and motivations but someone else might be even worse at figuring you out.
Not that much changes from when we are toddlers. As often as not when someone is being a jerk they are tired or upset about something unrelated. No one in this situation wants to admit that they are probably only upset because of a need for sleep, and no one wants to be told that they have to go to bed. That thing they are thinking about and having feelings about is really real and really important.