Pre-testing and post-testing is a commonly used method in Physics Education Research to assess student learning gains. It is well recognized in the community that timings and incentives in delivering conceptual tests can impact test results. However, it is difficult to control these variables across different studies. As a common practice, a pre-test is often administered either at or near the beginning of a course, while a post-test can be given either at or near the end of a course. Also, in conducting such tests there often is no norm as to whether incentives should be offered to students. Because these variations can significantly affect test results, it is important to study and document their impact. We analyzed five years of data that were collected at The Ohio State University from over 2100 students, who took both the pre-test and post-test of the Conceptual Survey of Electricity and Magnetism under various timings and incentives. We observed that the actual time frame for giving a test has a marked effect on the test results and that incentive granting also has a significant influence on test outcomes. These results suggest that one should carefully monitor and document the conditions under which tests are administered.