Software Testing Best Practices
By: Ram Chillarege
This report lists 28 best practices that contribute to improved software testing. They are not
necessarily related to software test tools. Some may have associated tools but they are
fundamentally practice. The collections represent practices that several experienced software
organizations have gained from and and recognize as key.
Every time we conclude a study or task force on the subject of software development
process I have found one recommendation that comes out loud and clear. "We need to adopt the
best practices in the industry." While it appears as an obvious conclusion, the most glaring lack of
it's presence continues to astound the study team. So clear is its presence that it distinguishes the
winners from the also-ran like no other factor.
The search for best practices is constant. Some are known and well recognized, others
debated, and several hidden. Sometimes a practices that is obvious to the observer may be
transparent to the practitioner who chants "that's just the way we do things." At other times
what's known in one community is never heard of in another.
The list in this article is focused on Software Testing. While every attempt is made to
focus it to testing, we know, that testing does not stand alone. It is intimately dependent on the
development activity and therefore draws heavily on the development practices. But finally,
testing is a separate process activity -- the final arbiter of validity before the user assesses its
The collection of practices have come frohm many sources -- at this point indelibly
blended with its long history. Some of them were identified merely through a recognition of what
is in the literatures; others through focus groups where practitioners identified what they valued.
The list has been sifted and shared with increasing number of practitioners to gain their insight.
And finally they were culled down to a reasonable number.
A long list is hard to conceptualize, less translate to implementation. To be actionable, we
need to think in terms of steps -- a few at a time, and avenues to tailor the choice to our own
independent needs. I like to think of them as Basic, Foundational, and Incremental.
The Basics are exactly that. They are the training wheels you need to get started and
when you take them off, it is evident that you know how to ride. But remember, that you take
them off does not mean you forget how to ride. This is an important difference which all too often
is forgotten in software. "Yeah, we used to write functional specification but we don't do that
anymore" means you forget to ride, not that you didn't need to do that step anymore. The
Basic practices have been around for a long time. Their value contribution is widely recognized
and documented in our software engineering literature. Their applicability is broad, regardless of
product or process.
The Foundational practices are the rock in the soil that protects your efforts against
harshness of nature, be it a redesign of your architecture or enhancements to sustain unforeseen
growth. They need to be put down thoughtfully and will make the difference in the long haul,
whether you build a ranch or a skyscraper. Their value add is significant and established by a few
leaders in the industry. Unlike the Basics, they are probably not as well known and therefore need
implementation help. While there may be no textbooks on them yet, there is plenty of
documentation to dig up.
The Incremental practices provide specific advantages in special conditions. While they
may not provide broad gains across the board of testing, they are more specialized. These are the
right angle drills -- when you need it, there's nothing else that can get between narrow studs and
drill a hole perfectly square. At the same time, if there was just one drill you were going to buy, it
may not be your first choice. Not all practices are widely known or greatly documented. But they
all possess the strength that are powerful when judiciously applied.
The next sections describe each of the practices and are grouped under Basics,
Foundational, and Incremental.
2. The Basic Practices
.Reviews and Inspection
.Formal entry and exit criteria
.Functional test - variations
.Automated test execution
Functional specifications are a key part of many development processes and came
into vogue with the development of the waterfall process. While it is a development
process aspect, it is critically necessary for software functional test. A functional
specification often describes the external view of an object or a procedure indicating the
options by which a service could be invoked. The testers use this to write down test cases
from a black box testing perspective.
The advantage of having a functional specification is that the test generation
activity could happen in parallel with the development of the code. This is ideal from
several dimensions. Firstly, it gains parallelism in execution, removing a serious
serialization bottleneck in the development process. By the time the software code is
ready, the test cases are also ready to be run against the code. Secondly, it forces a degree
of clarity from the perspective of a designer and an architect, so essential for the overall
efficiencies of development. Thirdly, the functional specifications become documentation
that can be shared with the customers to gain an additional perspective on what is being
Reviews and Inspection
Software inspection, which was invented by Mike Fagan in the mid 70’s at IBM,
has grown to be recognized as one of the most efficient methods of debugging code.
Today, 20 years later, there are several books written on software inspection, tools have
been made available, and consulting organizations teach the practice of software
inspection. It is argued that software inspection can easily provide a ten times gain in the
process of debugging software. Not much needs to be said about this, since it is a fairly
well-known and understood practice.
Formal Entry and Exit Criteria
The notion of a formal entry and exit criteria goes back to the evolution of the
waterfall development processes and a model called ETVX, again an IBM invention. The
idea is that every process step, be it inspection, functional test, or software design, has a
precise entry and precise exit criteria. These are defined by the development process and
are watched by management to gate the movement from one stage to another. It is
arguable as to how precise any one of the criteria can be, and with the decrease of
emphasis development, process entry and exit criteria went out of currency. However,
this practice allows much more careful management of the software development process.
Functional Test - Variations
Most functional tests are written as black box tests working off a functional
specification. The number of test cases that are generated usually are variations on the
input space coupled with visiting the output conditions. A variation refers to a specific
combination of input conditions to yield a specific output condition. Writing down
functional tests involves writing different variations to cover as much of the state space as
one deems necessary for a program. The best practice involves understanding how to
write variations and gain coverage which is adequate enough to thoroughly test the
function. Given that there is no measure of coverage for functional tests, the practice of
writing variations does involve an element of art. The practice has been in use in many
locations within IBM and we need to consolidate our knowledge to teach new function
testers the art and practice.
Many products today are designed to run on different platforms which creates the
additional burden to both design and test the product. When code is ported from one
platform to another, modifications are sometimes done for performance purposes. The net
result is that testing on multiple platforms has become a necessity for most products.
Therefore techniques to do this better, both in development and testing, are essential. This
best practice should address all aspects of multi-platform development and testing.
The idea of a Beta is to release a product to a limited number of customers and get
feedback to fix problems before a larger shipment. For larger companies, such as IBM,
Microsoft and Oracle, many of their products are used internally, thus forming a good beta
audience. Techniques to best conduct such an internal Beta test are essential for us to
obtain good coverage and efficiently use internal resources. This best practice has
everything to do with Beta programs though on a smaller scale to best leverage it and
reduce cost and expense of an external Beta.
Automated Test Execution
The goal of automated test execution is that we minimize the amount of manual
work involved in test execution and gain higher coverage with a larger number of test
cases. The automated test execution has a significant impact on both the tools sets for test
execution and also the way tests are designed. Integral to automated test environments is
the test oracle that verifies current operation and logs failure with diagnosis information.
This is a best practice fairly well understood in some segments of software testing and not
in others. The best practice, therefore, needs to leverage what is known and then develop
methods for areas where automation is not yet fully exploited.
(see internal betas)
The concept of a nightly build has been in vogue for a long time. While every build
is not necessarily done every day, the concept captures frequent builds from changes that
are being promoted into the change control system. The advantage is firstly, that if a
major regression occurs because of errors recently generated, they are captured quickly.
Secondly, regression tests can be run in the background. Thirdly, the newer releases of
software are available to developers and testers sooner.
. User Scenarios
. Usability Testing
. In-process ODC feedback loops
. Multi-release ODC/Butterfly profiles
. Requirements for test planning
. Automated test generation
As we integrate multiple software products and create end user applications that
invoke one or a multiplicity of products, the task of testing the end user features gets
complicated. One of the viable methods of testing is to develop user scenarios that
exercise the functionality of the applications. We broadly call these User Scenarios. The
advantage of the user scenario is that it tests the product in the ways that most likely
reflect customer usage, imitating what Software Reliability Engineering has for long
advocated under the concept of Operational Profile. A further advantage of using user
scenarios is that one reduces the complexity of writing test cases by moving to testing
scenarios than features of an application. However, the methodology of developing user
scenarios and using enough of them to get adequate coverage at a functional level
continues to be a difficult task. This best practice should capture methods of recording
user scenarios and developing test cases based on them. In addition it could discuss
potential diagnosis methods when specific failure scenarios occurs.
For a large number of products, it is believed that the usability becomes the final
arbiter of quality. This is true for a large number of desktop applications that gained
market share through providing a good user experience. Usability testing needs to not only
assess how usable a product is but also provide feedback on methods to improve the user
experience and thereby gain a positive quality image. The best practice for usability
testing should also have knowledge about advances in the area of Human Computer
In-Process ODC Feedback Loops
Orthogonal defect classification is a measurement method that uses the defect
stream to provide precise measurability into the product and the process. Given the
measurement, a variety of analysis techniques have been developed to assist management
and decision making on a range of software engineering activities. One of the uses of ODC
has been the ability to close feedback loops in a software development process, which has
traditionally been a difficult task. While ODC can be used for a variety of other software
management methods, closing of feedback loops has been found over the past few years to
be a much needed process improvement and cost control mechanism.
A key feature of the ODC measurement is the ability to look at multiple releases of
a product and develop a profile of customer usage and its impact on warranty costs and
overall development efficiencies. The technology of multi-release ODC/Butterfly analysis
allows a product manager to make strategic development decisions so as to optimize
development costs, time to market, and quality issues by recognizing customer trends,
usage patterns, and product performance.
“Requirements” for Test Planning
One of the roles of software testing is to ensure that the product meets the
requirements of the clientele. Capturing the requirements therefore becomes an essential
part not only to help develop but to create test plans that can be used to gauge if the
developed product is likely to meet customer needs. Often times in smaller development
organizations, the task of requirements management falls prey to conjectures of what
ought to be developed as opposed to what is needed in the market. Therefore,
requirements management and its translation to produce test plans is an important step.
This practice needs to be understood and executed with a holistic view to be successful.
Automated Test Generation
Almost 30% of the testing task can be the writing of test cases. To first order of
approximation, this is a completely manual exercise and a prime candidate for savings
through automation. However, the technology for automation has not been advancing as
rapidly as one would have hoped. While there are automated test generation tools they
often produce too large a test set, defeating the gains from automation. On the other,
there do exist a few techniques and tools that have been recognized as good methods for
automatically generating test cases. The practice needs to understand which of these
methods are successful and in what environments they are viable. There is a reasonable
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