When Should Testing Occur?

 “Testing should start early in the life cycle of development"?

 Studies have shown that most of the system errors detected during the testing phase originate in the early analysis phase. Therefore, software testing should start early in the system development process.

Defects detected later in the software lifecycle are lot costlier to fix then if fixed early in the lifecycle. 

Using the V-Model of testing, once the requirements are baselined, System testing plan ( or UAT ) and test cases should be prepared. This will also help in uncovering the gaps in requirements process. 

As you move forward and complete the Design, you should complete the Integration testing cases and also to some extent Unit test cases. 

Even if the project is in the requirement's stage, testing a project's requirements can be a useful and cost-effective way to prevent defects later on.

Early testing has following advantages:

1. Early preparation of test environment, thereby preventing any delays and unknown risks will have enough time to deal with.

2. If you complete test cases early you will have a baseline. If there are changes later , problem will be easy to detect by comparing it with baseline.

3. You will have time to Quantify the problem's scope.

4. You may find that few items may not be tested , since they may not be impacted. This input can cut down on your Testing phase.

5. There is usually tendency to  squeeze the testing time. This may impact Quality. But if you start testing early , you may not need to squeeze your time.