Manual Verify
Think like someone who uses this product: who are they, what are they trying to get done, and how could these changes affect them?
Choose workflows. Read the changes and identify the affected audience and tasks. Use judgment to pick realistic workflows, including nearby behavior that could break. Cover relevant error or edge cases without turning every change into a full product audit.
Use the product. Use a browser for web apps and iOS Simulator for iOS apps. For other tools, use the interface their users would use. Carry out the chosen workflows and compare what happens with what the user needs. Check that the result makes sense and is usable, beyond whether the action succeeds.
If login or another step needs the user, tell them exactly what to do and where, then resume once they finish. Continue any independent checks meanwhile. If the environment cannot support a needed check, report the gap.
Report what happened. Briefly state the workflows tested, expected and observed results, and any failures or gaps. Include screenshots or other evidence when useful. Base conclusions on what you exercised; distinguish untested behavior from passing checks.