Self-assessment
In 2012 I passed C2 level Cambridge English exam - CPE. Since then I am sure I have forgotten a lot. Mostly regarding vocabulary which is not used often as well as some specific pieces of grammar.
I took some online grammar tests mostly with the result of the C1 or C2 level and I believe that I have at least C1 level overall even though I am not able to test my speaking and writing online.
Listening: Usually, I can understand any kind of spoken language without any difficulties. Nevertheless, speaking with some native speakers /especially from New Zealand, Australia or Ireland) is a bit problematic at the beginning (sometimes for quite long) before I get used to their accent.
Writing: I believe I can express myself in clear and grammatically correct text, although I sometimes struggle with certain stylistic requirements. Provided that I know enough information about the given topic, I am able to write complex and extensive texts. I am also experimenting with creative writing courses at the moment.
Speaking: I can express myself fluently and spontaneously only with rare grammatical errors. I believe I can understand most idiomatic expressions and colloquialisms used in everyday conversations. However, I do not use all the structures and vocabulary I know in my spoken discourse and I mix British and American pronunciation.
Reading: I love reading and I can read with ease (except for complicated technical or legal materials) never mind how structurally or linguistically complex the texts are.