Written by Member
Software Testing Techniques
Introduction
Load testing generally refers to the practice of modeling
the expected
usage of a software program by simulating multiple users
accessing
the program's services concurrently. As such, this testing
is most
relevant for multi-user systems, often one built using a
client/server
model, such as web servers. However, other types of
software systems
can be load-tested also. For example, a word processor or graphics
editor can be forced to read an extremely large document;
or a
financial package can be forced to generate a report based
on several
years' worth of data. The most accurate load testing
occurs with
actual, rather than theoretical, results.
When the load placed on the system is raised beyond normal
usage patterns, in order to test the system's response at
unusually
high or peak loads, it is known as stress testing. The
load is
usually so great that error conditions are the expected
result, although no clear boundary exists when an activity
ceases
to be a load test and becomes a stress test.
There is little agreement on what the specific goals of
load testing are.
The term is often used synonymously with performance
testing, reliability
testing, and volume testing.
Testing
Load and Performance testing is to test software intended for a multi-user
audience for the desired performance by subjecting it with an equal amount
of virtual users and then monitoring the performance under the specified load,
usually in a test enviromnent identical to the production, before going live.
For example if a web site with a shopping cart is intended for 100 concurrent
users who are doing the following functions:
* 25 VUsers are browsing through the items and logging off
* 25 Vusers are adding items to the shopping cart and checking out
and logging off
* 25 VUsers are returning items previously purchased and logging off
* 25 VUsers are just logged in without any activity
Using various tools available to generate these VUsers the application is
subjected to a 100 VUser load as shown above and its performance is
monitored. The pass fail criteria is different for each individual organization
and there are no standards on what an acceptable criteria should be, across
the board.
It is a common misconception that these are record and playback tools like
regression testing tools, however it must be clarified that the similarity ends
just there. The Load testing tools work at the protocol level where as the
regression testing tools work at the GUI object level. To give an example
a regression testing tool will simulate a mouse click on an OK button on
the browser, but a load testing tool will send out the hypertext that the browser
will send after the user clicks the OK button, and again it will send out the
hypertext for multiple users each having a unique login ID and password.
Tools
Various tools are also available to find out the causes for slow performance
which could be in the following areas:
* Application
* Database
* Network
* Client side processing
* Load Balancer
Input
The following are useful inputs for load-testing a Web application:
- Performance-critical usage
scenarios
- Workload models
- Performance acceptance
criteria
- Performance metrics
associated with the acceptance criteria
- Interview feedback from the
designer or developer of the Web application
- Interview feedback from end
users of the application
- Interview feedback from the
operations personnel who will maintain and manage the application
Output
The main outcomes that load testing helps you to accomplish are:
- Updated test plans and test
designs for load and performance testing
- Various performance measures
such as throughput, response time, and resource utilization
- Potential bottlenecks that
need to be analyzed in the white-box testing phase
- The behavior of the
application at various load level
Approach for Load
Testing
The following steps are involved in load-testing a Web application:
Step 1 - Identify performance acceptance criteria
Step 2 - Identify key scenarios
Step 3 - Create a workload model
Step 4 - Identify the target load levels
Step 5 - Identify metrics
Step 6 - Design specific tests
Step 7 - Run tests
Step 8 - Analyze the results
Summary
Load testing helps to identify the maximum operating
capacity of the
application and any bottlenecks that might be degrading
performance.
The basic methodology for performing load testing on a Web
application is to identify the performance-critical key
scenarios; identify
the workload profile for distributing all the load among the
key scenarios;
identify metrics that you want to collect in order to verify
them against
your performance objectives; create test cases that will be
used to simulate
the load test; use tools to simulate the load according to
the test cases and
capture the metrics; and finally, analyze the metrics data
captured during
the tests.
