I did two practice tests. I did two practice exercises.

In general, "practice" is uncountable. But you can use it as an abbreviation for something like "a practice session" or a "practice test". As long as the reader understands what you're talking about, you can treat it as countable and say "practices" if it's used as a plural form.

Practices can be countable yes. However, it becomes a bit confusing when you phrase the idea the way you have: "I did two practices today...". You'd have to add the 's' in order to make it plural. A more adequate way to form the sentence would be : "I did two practice sessions(or papers/assignments/tasks) today", all of which will be in a more understandable plural form.

Hello Lilian, Well done but your sentence doesn't quiet make sense. You could phrase the start of your sentence: "I practiced twice today", as for the second half, practice is a verb (you do it) not a noun (thing/object) so you can not hand it to the teacher.