What is test requirement?

The concept of test requirement is relatively simple. For example, there is an applet calculating square root, if we input one number which is greater or equal to zero, it can give a result; if we input one number which is less than zero, the applet will point out that the input is wrong. The engineers who have read The Art of Software Testing will immediately associate with boundary value. To test the numerical value of zero; to test the negative which is close to zero, these are two specific test requirements.

In an even more complex application, you may make a list of the projects you intend to test. However, these test requirements will not use specific test data. For example, if there is a bank transaction procedure, one test requirement is trying to pay the customer with a negative; the other test requirement is that the customer in the transaction doesn’t exist, and so on. You have a series of test requirements, but they don’t indicate the specific number or data, such as the customer’s name.

The next step of test is to choose imput value or test data to satisfy these test requirements. A simple test case may satisfy several test requirements at a time. It is the ideal situation that one test case can satisfy several test requirements at a time, but it costs too much. Another way is to design a single test case for each test requirement, then we don’t need to consider those complex test cases, but the ability of these relatively simple test cases to discover defects will decline.

There is an example of test requirement: To test the inserting operation of Hashtable with the test requirements as follows:
1) Insert a new entry;
2) Insert failure - Entry has already exists;
3) Insert failure – Table is full;
4) Hashtable is empty before inserting.

These are the test requirements rather than test cases, because they haven’t described the inserted elements. In addition, you cannot immediately begin writing the use cases, as if we cannot immediately do the coding work after finishing software requirement. We need to review the test requirements to make sure they are correct and no requirement is omitted.

This is only one aspect of understanding test requirement.

Test requirement should include two aspects:
1. Determine what should be tested;
Test requirement about the product to be tested. This is to address the issue of product providing features to better fulfill the test, which is also what we call testability requirement.