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WHAT IS SOFTWARE TESTING?
Software testing is a process of verifying and validating that a
software application or program
1. Meets the business and technical requirements that guided
its design and development, and
2. Works as expected.
SOFTWARE TESTING HAS THREE MAIN PURPOSES:
VERIFICATION, VALIDATION, AND DEFECT FINDING.
The verification process confirms that the
software meets its technical specifications.
The validation process confirms that the
software meets the business requirements.
A defect is a variance between the expected
and actual result.
WHY DO SOFTWARE TESTING?
In February 2003 the U.S. Treasury Department mailed 50,000 Social
Security checks without a beneficiary name. A spokesperson said that the
missing names were due to a software program maintenance error.
In July 2001 a “serious flaw” was found in off-the-shelf software that had
long been used in systems for tracking U.S. nuclear materials. The software
had recently been donated to another country and scientists in that country
discovered the problem and told U.S. officials about it.
In October 1999 the $125 million NASA Mars Climate Orbiter—an
interplanetary weather satellite—was lost in space due to a data conversion
error. Investigators discovered that software on the spacecraft performed
certain calculations in English units (yards) when it should have used metric
In June 1996 the first flight of the European Space Agency's Ariane 5 rocket
failed shortly after launching, resulting in an uninsured loss of
$500,000,000. The disaster was traced to the lack of exception handling
for a floating-point error when a 64-bit integer was converted to a 16-bit
WHAT DO WE TEST?
Testing can involve some or all of the following factors.
Functional design requirements
Technical design requirements
Systems administration standards and restrictions
Professional or trade association best practices
Cultural issues and language differences
WHO DOES THE TESTING?
Software testing is not a one person job. It takes a
team, but the team may be larger or smaller
depending on the size and complexity of the
application being tested. The programmer(s) who
wrote the application should have a reduced role in
the testing if possible.
Testers must be cautious, curious, critical but non-
judgmental and good communicators.
SOFTWARE TEST PLANNING
The quality of Software testing effort depends
on the quality of quality of Software Testing
Planning. Software testing planning is very
critical and important part of Software Testing
BELOW ARE SOME QUESTIONS AND SUGGESTIONS FOR SOFTWARE
- Have you planned for an overall testing schedule and the personnel required and
associated training requirements?
Have the test team members been given assignments?
Have you designed at least one black-box test case for each system function?
- Have you designed test cases for verifying quality objectives/factors (e.g. reliability,
- Have you designed test cases for verifying resource objectives?
- Have you defined test cases for performance tests, boundary tests, and usability
- Have you designed test cases for stress tests (intentional attempts to break
- Have you designed test cases with special input values (e.g. empty files)?
- Have you designed test cases with default input values?
- Do all test cases agree with the specification of the function or requirement to be
- Have you sufficiently considered error cases? Have you designed test cases for
invalid and unexpected input conditions as well as valid conditions?
- Have you defined test cases for white-box-testing (structural tests)?
- Have you stated the level of coverage to be achieved by structural tests?
- Have you unambiguously provided test input data and expected test results or
expected messages for each test case?
- Have you documented the purpose of and the capability demonstrated by each test
- Is it possible to meet and to measure all test objectives defined (e.g. test
- Have you defined the test environment and tools needed for executing the software
- Have you described the hardware configuration resources needed to implement the
designed test cases?
- Have you described the software configuration needed to implement the designed
A good test has a high probability of finding an error. To achieve
this goal, the tester must understand the software and attempt
to develop a mental picture of how the software might fail.
A good test is not redundant. Testing time and resources are
limited. There is no point in conducting a test that has the
same purpose as another test. Every test should have a
A good test should be “best of breed”. The test that has the
highest likelihood of uncovering a whole class of errors should
A good test should be neither too simple nor too complex. Each
test should be executed separately
THE TEST PLAN
The test plan is a mandatory document. You
can’t test without one. For simple, straight-
forward projects the plan doesn’t have to be
elaborate but it must address certain items.
SOFTWARE TESTING PRINCIPLES
Testing must be done by an independent party.
Testing should not be performed by the person or team that developed
the software since they tend to defend the correctness of the program.
Assign best personnel to the task.
Because testing requires high creativity and responsibility only the best
personnel must be assigned to design, implement, and analyze test
cases, test data and test results.
Testing should not be planned under the tacit assumption that no errors
will be found.
Test for invalid and unexpected input conditions as well as valid
The program should generate correct messages when an invalid test is
encountered and should generate correct results when the test is valid.
The probability of the existence of more errors in a
module or group of modules is directly proportional to the
number of errors already found.
Testing is the process of executing software with the
intent of finding errors.
Keep software static during test.
The program must not be modified during the
implementation of the set of designed test cases.
Document test cases and test results.
Provide expected test results if possible.
A necessary part of test documentation is the
specification of expected results, even if providing such
results is impractical.
SOFTWARE TESTING GOALS
To locate and prevent bugs as early as possible
To perform all Tests according to the
Requirements, in the most effective and
To bring the software product to a level of
quality that is appropriate for the client
TEST STRATEGIES FOR CONVENTIONAL
Unit testing focuses verification effort on the
smallest unit of software design—the software
component or module. Using the component-
level design description as a guide, important
control paths are tested to uncover errors
within the boundary of the module.
It is of two types:
Top-down integration testing is
an incremental approach to
construction of program
structure. Modules are
integrated by moving
downward through the control
hierarchy, beginning with the
main control module (main
testing, as its name implies,
begins construction and
testing with atomic modules
(i.e., components at the
lowest levels in the program
components are integrated
from the bottom up,
processing required for
components subordinate to
a given level is always
available and the need for
stubs is eliminated.
Regression testing means rerunning test cases
from existing test suites to build confidence
that software changes have no unintended
At the culmination of integration testing,
software is completely assembled as a
package, interfacing errors have been
uncovered and corrected and a final series of
software tests—validation testing—may begin.
Validation can be defined in many ways, but a
simple (albeit harsh) definition is that validation
succeeds when software functions in a manner
that can be reasonably expected by the
VALIDATION TESTING CRITERIA:
The alpha test is conducted at the developer's site by
a customer. The software is used in a natural setting
with the developer "looking over the shoulder" of the
user and recording errors and usage problems. Alpha
tests are conducted in a controlled environment.
The beta test is conducted at one or more customer
sites by the end-user of the software. Unlike alpha
testing, the developer is generally not present.
System testing is actually a series of different
tests whose primary purpose is to fully exercise
the computer-based system. Although each test
has a different purpose, all work to verify that
system elements have been properly integrated
and perform allocated functions.
Recovery testing is a system test that forces the
software to fail in a variety of ways and verifies that
recovery is properly performed.
Security testing attempts to verify that protection
mechanisms built into a system will, in fact, protect
it from improper penetration. To quote Beizer "The
system's security must, of course, be tested for
invulnerability from frontal attack—but must also
be tested for invulnerability from flank or rear
Stress testing executes a system in a manner that demands
resources in abnormal quantity, frequency, or volume. For
example, (1) special tests may be designed that generate ten
interrupts per second, when one or two is the average rate, (2)
input data rates may be increased by an order of magnitude to
determine how input functions will respond, (3) test cases that
require maximum memory or other resources are executed, (4)
test cases that may cause thrashing in a virtual operating
system are designed, (5) test cases that may cause excessive
hunting for disk-resident data are created. Essentially, the
tester attempts to break the program.
Performance testing is designed to test the run-
time performance of software within the
context of an integrated system. Performance
testing occurs throughout all steps in the