Passing the practice exams does not guarantee that you'll also pass the actual exams. You should remember that there are lots of materials in the study guides and other references, and questions can be tweaked, rephrased or taken from other sections of the tasks not covered by your practice exams. As long as you have mastery and in-depth knowledge of the relevant subject matter, then it is safe to say that you will pass the actual exams. The only way to do this is to read and re-read the materials until all the concepts and supply management applications seep entirely into your brain. Familiarity and concept recall with the study materials are essential factors in achieving a passing mark during the actual exams.
Hope this helps.