Software Testing
Testing with a Purpose
Software testing is performed to verify that the completed software
package functions according to the expectations defined by the
requirements/specifications. The overall objective to not to find every
software bug that exists, but to uncover situations that could
negatively impact the customer, usability and/or maintainability.
From the module level to the application level, this article defines the different types of testing. Depending upon the purpose for testing and the software requirements/specs, a combination of testing methodologies is applied. One of the most overlooked areas of testing is regression testing and fault tolerant testing.
Definition of Testing Types
Functional Testing
Module testing verifies that individual software unit performs as
expected according to the requirements using a small subset of possible
input parameters. At the application level, testing verifies that the
entire application functions together according to the requirements.
Example:
- Passing in real world parameters as well as valid but unusual parameters.
Parametric Testing
At the module level, testing verifies that individual software unit
performs as expected according to the requirements for the full range
of valid input parameters. Example:
- Passing in each parameter at its minimum, maximum and median values, as well as passing in parameters at the minimum and maximum values at the same time.
Fault Tolerant Testing
Module testing verifies that individual software unit does not
perform in a detrimental or unexpected manner for illegal or
out-of-range input parameters. At the application level, testing
verifies that the entire application functions together in a graceful
manner according to the requirements when presented with unexpected
and/or out-of-range values. Example:
- Passing null pointers and the full range of possible values for each parameter.
Integration Testing
Integration testing is an additional step that is used when
different sub-systems are being developed simultaneously by independent
developers. It verifies that the parameters passed between sub-systems
are being handled correctly. Example:
- Passing null pointers and the full range of possible values for each parameter.
Regression Testing
Regression testing is retesting sub-systems/modules/units to insure
that modifications to one sub-system/module/unit does not cause
unexpected results in another sub-system/module/unit. This is also known
as ripple effect testing.
Why is Regression Testing Necessary?
Regression testing is necessary because many times modifications in
one part of the code cause unexpected problems in a "totally unrelated"
area of the code.
Example scenario:
A video driver was released for the Diamond Stealth video board.
Complaints started to come in that HP InkJet drivers were crashing when
doing a print preview. It was discovered that the print preview
functionality calls the video board's font rasterizing functions to
generate the print preview.
A bug in the video boards font rasterizing function was causing a memory fault when called by the HP print driver. This caused the error to appear like it was in the printer driver and not the video driver.
Summary
Testing allows developers to deliver software that meets
expectations, prevents unexpected results, and improves the long term
maintenance of the application. Depending upon the purpose of testing
and the software requirements, the appropriate methodologies are
applied. Where possible, testing can be automated (a topic for another
discusssion).
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