The SOPI (Simulated Oral Proficiency Interview) and the WPA (Writing Proficiency Assessment) are language assessments carried out by the Stanford Language Center, designed to measure the oral and writing proficiencies of students who take first- and second-year (and some third-year) -LANG courses. Both assessments measure what students can do functionally with the language, and consist of real-life speaking and writing tasks.
The SOPI takes 25-45 minutes to complete and is given in the Digital Language Lab in Meyer Library; the WPA, 30-45 minutes, in the regular classroom; the eWPA is given in a different building (see the calendar link above). Each is given during a regular class hour. Tasks are similar to the types of hands-on speaking and writing activities students routinely do in and for class throughout the quarter, since these reflect the functional objectives of the course.
For that reason, the best way to prepare is to practice those objectives through regular and active participation in your language course. Some SOPI and WPA tasks will be easier, others more challenging. Regardless, the important thing is to:
Speak as much and as well as you can, and show what you can do.
Write as much and as well as you can, and show what you can do.
There is no provision for make-up tests for the WPA or eWPA.