Solfeggio is composing music. Generally, you can sing several bars, with or without melody (if the test is difficult, you will write all kinds of intervals and rhythms into an ugly and awkward solfeggio practice, and it depends on your basic skills if you are completely out of tune).
There are many test items for ear practice, such as monophonic singing (playing a note and you sing along), polyphonic singing, chord discrimination, chord decomposition, rhythm memory, melody memory and so on. See what people want to test.
Composers create music, just like writers write poems and novels, and there is a system of expression and expression, that is, music language. Music language includes many elements: melody, rhythm, beat, speed, dynamics, range, timbre, harmony, polyphony, mode, tonality and so on. The ideological and artistic beauty of a musical work can only be expressed through various elements.