“The best workout is a race,” goes the old saying. Using races to break up the monotony of training is an excellent idea and a good way to overcome thinking about every race the be-all and end-all of your running. If you get nervous before important races, using races as workouts gives you more practice at going through race-day logistics calmly.
There are lots of options here: Jump in a 5K as a tempo run. Experiment with finishing fast by running the first half of a 10K at tempo pace, then picking up the pace over the second half. Use a 10-miler or half marathon as a venue for a marathon-pace run where you can practice taking fluids at race pace and running in a large pack.