Saturday, August 9, 2008

Development Models and the impact on Testing

During my career as tester I learned that development methods have impact on testing. Also when sometimes a tester is working based on a test method it has impact on the success of the development method.

In books related to software testing often an approach is defined which is based no the Waterfall method. In the newer books they adjust that method to make it fit for incremental and iterative methods. Sometime this is done by only mentioning that it also works for other approaches.

In this Blog I'm trying to give some information about 3 development streams. It might not be completely perfect but I think it might be useful for the readers to give a picture how I see things. While I already know I want to write, I also know that this article will be much longer then I normally write. To miss information I decided not to split this topic in several other postings. Therefore I will give you some table of content:
- 3 approaches of development
- How development methods are linked to these models
- Short overview benefits and disadvantages per development method
- Overview how other models are related to these methods
- Impact towards software testing.

3 approaches of development
In general you have 3 development approaches. Waterfall, Incremental and Iterative (Evolutionary).
For more information you might check out the links which refer to description on Wikipedia.

In short these approaches can be described as following:
Waterfall approach: The whole system will be implemented at once;
Incremental approach: The system is divide is several steps, and is implemented in that order. Once a step is implemented you can not go back to a previous step to change functionality or do some "refactoring";
Iterative approach (Evolutionary): This is an approach were you continue development towards a final system. You are able to go back and change the code of the previous iteration. every iteration delivers a better system, even without adding new functionality.

How development methods are linked to these models
Often several types of development are called to be a variant on Agile Development, I rather prefer to keep speaking in terms of approaches. In this case Agile belongs to the more Evolutionary approach. Sometimes an approach belongs based on the actual implementation to either Incremental or Iterative. In that case you should not only look at the name of the development method like RUP or DSDM. You also have to investigate how that method is implemented. Perhaps the following picture gives some overview.

Short overview benefits and disadvantages per development method
In the last few years we tending to neglect Waterfall-approaches and claiming that methods as RUP, XP and Agile are always better. Only in some situations it is better to play save then take the risk of using methods you don't control on a level which is necessary. Mostly systems which has a long life-time like aerospace systems, life care systems or systems where you are a strong market leader and those don't change that much. I could be wise to use for these systems a waterfall approach. In the figures below an overview is given about the benefits and disadvantages of the 3 approaches. I know they are not complete. Still it can be handled as a guideline.

Overview how other models are related to these methods
To understand the impact of these approaches on Software Testing you have to understand how an approach effects the organization. To get a short overview of this I took several other models and views which can represent an organization.
- Organizational Model: Documentation about the organizational processes, procedures and activities;
- Information Model: Documentation how the organizational processes are supported/executed;
- Data Model: Documentation about the kind and location of information used;
- Process Model: Documentation how data is processed to support the pervious models .

- Conceptual/Logical View: High level view of the organization;
- Physical/Technical View: View of the architectural and informational representation of the system;
- Implementation View: How the system should be implemented in the organization.

In the tables below I tried to translate the development approaches towards the impact on documentation using several other models and views. To visualize this I used several colors.

When a certain cell is colored Green, then during the project this will not change much after it is finished. When the color is Yellow, there is a small chance it will change. The color Orange represents an obvious chance of change and the color Red: there will be changes.

The situation here is that when a chance occurs/ is made. The "defined" steady objects might also change when it is a result of new awareness. When this happens the test cases will change because they are built based on this documentation. Because changing documentation in previous steps takes time it gives an impression how steady the development process will be and therefore the test process. On the other hand it also give a feeling for ability to adapt your test process on those changes.

Views for a Waterfall-approach

Views for a Incremental-approach

Views for a Iterative-approach

Impact towards software testing.
Below you find a short overview of the characteristics of the development approach, their impact on the project development process and the impact on the test process. Keep in mind that these items are not complete. It is just mentioned to serve as a guideline. There is always a dependency towards the actual implementation of the development method.

I hope this blog gives you more feeling how development processes are impacting the test process. Bare with me when I made some miss interpretations. It came never to my mind to make a statement about which approach is better then the other. It should help you as a guideline to identify impact on your own process and therefore helping to identifying risks and controlling those.

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