How to write this test case?

Question

I have never worked as a QA but have some interest in the field and I received a task for an entry position which requires me to write a test case to fulfil this requirement (it's a messaging service):

1.Every person can have unlimited conversations and unlimited messages in a conversation.

There were a few other specifications which were simpler and I followed the test case, test scenario, expected results format of writing them, but I am unsure how would one test if something works for unlimited amount of data, in this case, infinite messages?

Answer 1

1. Every person can have unlimited conversations and unlimited messages in a conversation.

These are two use cases:

1. Every person can have unlimited conversations
2. Every conversation can have unlimited messages.

As one of the testing principle is :

Exhaustive testing is not possible .meaning you cannot test all the possibility for a system as the combination would be extremely large.

So in this case (infinite) is a uncountable and unachievable use case, what you can do as a quality enthusiast is to.

1. Understand your userbase. See what is the average number of conversation kept in the app by your user. Say you figured out that on an average users will keep only last 100 conversations. ( If there is no average see what is the maximum conversation kept eg: User b had 10000 conversation which is the largest ever reported )

2. Understand your userbase. See what is the average number of messages per conversation kept in the app by your user. Say you figured out that on an average users will keep only last 100 messages per conversation. ( If there is no average see what is the maximum message kept eg: User b had 10000 message in a conversation which is the largest ever reported )

3. Now test n*2 times messages and conversation , where n is the max message or conversation.

4. Most important: Each time create new n*2 message and conversation , don't clear old messages and converstaions. This gives you ever growing database which you can validate for ( near to infinite usecase) .

Update:

You can also choose to add N*2 messages to more than 1 conversation , say first 5 conversation ever added. This ensures that system works fine even when there are multiple conversations with ever growing near to infinite messages

Answer 2

unlimited conversations and unlimited messages

something works for an unlimited amount of data, in this case, infinite messages

These two statements may mean different things.

There is no such thing as an infinite number of entities in a computer system because computers have physical limitations, in terms of memory, storage, processing.

What you can do is to create testing charters detailing how you can explore these limitations.

For instance,

Explore the application with the phone XYZ To discover how it handles keeping an extreme number of message loaded

Or

Explore the backend service to discover how it behaves when an extreme number of messages are stored for a single user

Then during your exploration, you will use your skills to try to force the target to these extreme conditions. Later you debrief the people who need this information so they can make decisions.

Test cases are good documentation for situations where you know what you want to know. You have a specific routine and a known expected result.

This is called checking. Testing is an open-ended performance to discover facts we don't know. Testing is exploration. (More about Testing versus Checking here)

Answer 3

You can't.

I see this as a question which should introduce performance / stress tests to determine the number of conversations / messages which still allows user to use the application and number of conversations / messages which the system can actually handle.