We are rapidly approaching the point when most students will take most standardized tests online. Of course, the nature of the computer adaptive test is that they are far from standard, as the questions students answer correctly or incorrectly are likely to determine the level and complexity of their next question. I can't suggest any tools that are computer adaptive in that way. But there are several online options for preparing students to take online assessments.
Practice tests available online indicate new tests will likely include multiple choice questions with more than four choices, questions with more than one correct answer, listening passages, questions where students have to explain why they chose that answer, and even questions in a grid format.
Obviously, the first hurdle in preparing students for online testing spaces is getting them online. I can't help you much with that. The access part is up to you. Once you get students online though these are some tools you can use to approximate the experience they may have with an online test. All of them can be customized to the content you are teaching, so none of this should be viewed as test prep. These are just ways of adding more online assessments to your curriculum, so your students will feel comfortable, reading, writing, and thinking critically with a screen and a keyboard.
Thinking with a keyboard. Many students who are not used to using computers struggle to compose writing pieces on a keyboard. Any platform that asks students to type their answers will help with this. Try starting with short answers and working up to longer pieces. If your usual method is to have students write drafts by hand and then type them up, you should consider adding more opportunities for students to compose writing directly on the computer.
These are a great way to introduce students to online assessments. You can create multiple choice questions, as well as a variety of other question types. The one I want to be sure my students practice is a checkboxes question with more than one correct answer. Consider asking your students for the definition of a word that has more than one definition. I made a sample form with a few examples of the kinds of questions you can ask with a Google Form. (Ignore the content, focus on the format.) Paragraph answers in Google Forms are a place students can practice writing answers on the computer. You can also embed pictures and videos into a Google Form for visual literacy practice and some listening practice. More about Google Forms
Listening passages, where the student hears the text, but does not read it are another type of assessment I've seen on practice tests. To give students practice with this we need to give students things to listen to. TED talks are popular, but the video component means it's not purely audio. Listen Current is a site that creates curriculum materials to match audio content from NPR. With a wide range to choose from, there is bound to be material that matches the content you are teaching and gives students practice with listening.
Reading from a screen is another skill students may need to practice. Newsela.com is a way to give students practice reading non-fiction and for many of the articles there are also quizes that give students more experience with online assessment. (And don't miss the lexile level adjustment buttons.)
Other Useful Tools
There is a proliferation of online tools teachers can use to customize online formative and summative assessments, give students practice reading on line, and encourage a digital comfort zone that will reduce the technical challenges of measuring student achievement with computerized assessments.
Socrative, Nearpod, and Formative