As reviewed in Roediger & Karpicke - 2006 - The Power of Testing Memory, experiments which successfully demonstrate the testing effect usually use retention intervals of several days or longer. When tests are administered immediately, more studying may be better than more testing (see also Worked example effect).
Roediger & Karpicke - 2006 - The Power of Testing Memory
Leahy et al. - 2015 - High Element Interactivity Information During Problem Solving may Lead to Failure to Obtain the Testing Effect in experiments 1 and 2, they find an inverted testing effect when testing is immediate