The type of test I give depends on the kind of class I am giving. If it is a conversation class, I base my evaluation on conversational skills, and would only give an oral evaluation. If it is a regular class I usually give both a written and oral evaluation.
If I give an oral test, I generally start off with asking questions with the verb to be and to have.
Questions like:
What is your name?
Can you spell it for me.
Where to you live
Do you have (pets, children) tell me about them.
I then progress through the tenses and evaluate them on that.
Simple Present - Give me your daily routine
Present Continuous - now and future questions (pictures)
Past - What did you do yesterday.
I go on like this until I am able to find the proper level. If I see, a person is unable to go further I do not continue going to higher levels.
With the written test I use a placement test.
I would agree with Newuser that you can get good placement tests from books.
When this is finished I place them into different level groups, according to the test they have taken.