It depends upon the type of company (and whether small or large) you are taking the test with. Plus how well they have written the test but usually they'll get you to either edit a page or follow some instructions to create a webpage.
Or they might even give you some written or multi-choice questions too. Alternatively they might ask you, what you think is wrong with their 'current website' and how you'd alter the design, etc.
If you are new to coding you might have problems with the test. Though obviously you have got to interview stage so there was something they liked about you or they are testing a large number of people.