Find the smallest useful debugging example

Remove everything unrelated to the failing behavior. A plain shape, one input and a single update rule often reveal an issue more clearly than a full level.

Write the expected result and the actual result beside the example. Record the runtime and repeat the same input sequence after each change.

Continue the study

Work through a small code example, make one deliberate change and record the effect. The reading links below connect this exercise with animation, input and retro game design.