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Principles of Software Testability

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John Bainbridge

May 27, 1994, 7:15:03 AM5/27/94

Gang Luo

May 27, 1994, 10:16:06 AM5/27/94

Can someone tell me the definition of the Software Testability ?
Is the Testability a kind of software metrics ?

G. Luo

James Bach

May 26, 1994, 4:40:41 PM5/26/94
I'm trying to improve this list. Any comments are appreciated.

Principles of Software Testability


"The better it works, the more efficiently it can be tested."

* The system has few bugs (bugs add analysis and reporting overhead to
the test process).
* No bugs block the execution of tests.
* Product evolves in functional stages (allows simultaneous
development and testing).


"What you see is what you test."

* Distinct output is generated for each input.
* System states and variables are visible or queriable during
* Past system states and variables are visible or queriable (e.g.,
transaction logs).
* All factors affecting the output are visible.
* Incorrect output is easily identified.
* Internal errors are automatically detected through self-testing
* Internal errors are automatically reported.
* Source code is accessible.


"The better we can control the software, the more the testing can be
automated and optimized."

* All possible outputs can be generated through some combination of
* All code is executable through some combination of input.
* Software and hardware states and variables can be controlled
directly by the test engineer.
* Input and output formats are consistent and structured.
* Tests can be conveniently specified, automated, and reproduced.


"By controlling the scope of testing, we can more quickly isolate
problems and perform smarter retesting."

* The software system is built from independent modules.
* Software modules can be tested independently.


"The less there is to test, the more quickly we can test it."

* Functional simplicity (e.g., the feature set is the minimum
necessary to meet requirements)
* Structural simplicity (e.g., architecture is modularized to limit
the propagation of faults)
* Code simplicity (e.g. a coding standard is adopted for ease of
inspection and maintenance)


"The fewer the changes, the fewer the disruptions to testing."

* Changes to the software are infrequent.
* Changes to the software are controlled.
* Changes to the software do not invalidate existing tests.
* The software recovers well from failures.


"The more information we have, the smarter we will test."

* The design is well understood.
* Dependencies between internal, external and shared components are
well understood.
* Changes to the design are communicated.
* Technical documentation is instantly accessible.
* Technical documentation is well organized.
* Technical documentation is specific and detailed.
* Technical documentation is accurate.

James Bach
"The Data Guy"
Languages Quality Assurance
Borland International, (408)431-1476

James Bach

May 27, 1994, 9:29:26 PM5/27/94
Gang Luo (gl...@csi.uottawa.Ca) wrote:

: Can someone tell me the definition of the Software Testability ?

: Is the Testability a kind of software metrics ?
: Thanks.

Software testability is simply how easily it can be tested. Since
testing is so profoundly difficult, it pays to know what can be done to
streamline it. Sometimes that programmers are willing to do things that
will help the testing process. I'd like to have a checklist of possible
design points, features, etc. to use in negotiating with them.

There are certainly metrics that could be used to measure testability in
most of its aspects.

Sometimes, testability is used to mean how adequately a particular set of
tests will cover the product. It's also used by the military to mean how
easily a tool can be checked and repaired in the field. Those two
meanings are not the same as *software testability*.

James Bach | Section Chairman, Monterey Bay ASQC |
Senior Staff Engineer | Chapter Chairman, |
Languages Quality Assurance | Silicon Valley Software Quality |
Borland International | Association, Santa Cruz Chapter |

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