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Performance Testing - Scripting - Part 1

Web applications will typically follow n-tier architecture, i.e. presentation layer, business logic layer, data access layer, data layer, external interfaces etc. But a website will mostly static pages, may be with javscript. The entry and exit to websites is unpredictable, as every page is a potential entry and/or exit, they are all independent. I a web application (webapp), the sequence of tasks one does is very important, to complete a business transaction. Hence there is a difference between load testing a website and load testing a webapp. As we saw in the previous post, the very first step is to identify the most frequently used scenarios and the steps for those scenarios. From that point, we need to focus on scripts.

Every load test tool provides recording feature. This is the most economical, easy and powerful way of scripting. First the tester must record the sequence of operations, as one user does. This means, start recording, start doing the business transaction steps on the application. The tool will record all the requests and responses, going to server and coming back from the server, using an internal proxy. Ideally every load test tool sniffs the request/response between the browser and the server. The request may be a get or post or ajax request. The tool will identify the url, the query string parameters for the request and will identify the server response data and redirection pages. Soon after recording, if we replay the script, the tool must be in a position to send the request to the server.

Mere recording and replaying will not solve many business rules. Some apps will require unique data, some need random data, some need advanced correlation and that is what we must do as the next step with the recorded script. Also, it is better we organize the requests under folders/containers. This will help towards easy maintenance of the scripts. For example, if our sequence of operations look like the following,

Go to home page
Fill userid and password, login
Navigate to items page
Load items list grid
Select an item and edit
Enter new details and save
Refresh items grid

It is better to organize the same like this.

- Initialization
- Go to home page
- Fill userid and password, login
Items Grid Load
- Navigate to items page
- Load items list grid
Modify Item
- Select an item and edit
- Enter new details and save
Items Grid Refresh
- Refresh items grid
- Logout

Once the requests/steps are organized, the next step is to provide proper data to the script. We cannot use the same data we gave during recording. There are 2 parts to the data - static data, dynamic data. Static data is different data supplied/typed by the user on the screen, dynamic data is the data that server sends back to the screen. Providing static data is called parameterization and handling dynamic data is called correlation.

Static data can be provided thru variables. Tools provide variable manager module. We can create a variable and load the variable with different values, at run time. Some data that we may often use, can be obtained from the system itself, such as current date and time, user name, machine name, random number, random text, etc.

Some data will be application specific. This data will have dependencies on other application data as well. For this, we usually create a file to have such data and modify the hard coded data values in the script, to use the data variables. The variables will be mapped to the file and specific column in that file. This is very similar to data driven tests in functional test automation.

For example if item creation page requires item code, item name, UOM, price as user supplied data, create a csv file like this.

1001,Maxx Soap,NOS,18.90
1002,Vixor Biscuits,PCK,12.60
1099,Brainee Rice,KGS,14.50

Create a variable in the tool (say myItemData) and map that to this file.

In the script, replace the hard coded values with
myItemData.ITEMCODE, myItemData.ITEMNAME, myItemData.UOM,
myItemData.PRICE. During run time, the tool will read the data from this file and supply the values from the respective columns to the right variables. Usually, the tools will read lines sequentially and send that to the script. This can be changed as well. We will see these in the next post. Stay tuned.
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