CareerCup

Are you serious? There will be thousands (if not tens of thousands) of test cases needed to cover Amazon site.

Let us assume that we do NOT need to write unit tests (developers' responsibility), we are left now with:
- Functional
- Performance and scale
- Localization
- Tests in production
- Security Testing

Functional Tests:
Let us start with defining the functionality broadly:
- Main webpage
> Ads
> Featured products
> Products for individuals
> Menu for categories
- Product ratings
- Product categorization
- Clickstream management
- Product ranking
- Order management
- Payment systems
> Different modes of payments
> Amazon Prime credit cards management
- User profiles management
- Auto emailing of recommendations for users
- Partner programs, products from third parties
- Price comparisons from competitors. Realtime access to their inventories
- ... and list of features continues


Let us now focus only on ads. It will be a full fledge system in its own right, which will consist of features like registration of companies, the keywords/products they are interested in, the payment for ad placement, the display of ads and the tracking on clicks on each ad. Let us remove any dispute management from the scope for simplicity for now.

For each of the above, we can provide test cases like:
- Ad creation using picture
- Ad creation using text only
- Ad creation using both text and picture
- Test for the size limit of picture
- Test for size limit of text
- Empty ad creation test (no text or picture provided).
- Ad display on basis of provided criteria test
- Test for preview of picture
- Click detection on ad.
- Money deduction on clicks
- Simultaneous clicks on the ad from three clients (concurrency testing). Ensure correct amount of funds get deducted for customer.
and so on ...

i guess best way to start is list down all the types of testing required to be done for the given scenario, and think about test cases for those testing types one by one.