Functional Testing

Definition

Functional testing is the system testing of an integrated, blackbox, [partial] application against its operational (i.e., functional) requirements.

The typical goals of functional testing are to:

Cause the application to fail to meet its operational requirements so that the underlying defects can be identified, analyzed, fixed, and prevented in the future.

The typical objectives of functional testing are to:

Partially validate the system (i.e., to determine if it fulfills its operational requirements).
Cause failures concerning the operational requirements that help identify defects that are not efficiently found during unit and integration testing.
Report these failures to the development teams so that the associated defects can be fixed.
Help determine the extent to which the system is ready for launch.
Help provide project status metrics (e.g., percentage of use case paths successfully tested).
Provide input to the defect trend analysis effort.

Typical examples include functional testing of an application that is:

Software only.
A system including software, hardware, and data components.
Embeded within another system (e.g., flight-control software, cruise-control software).
Client/server or n-tier distributed.
A research prototype that will not be placed into service.
Business-critical or safety-critical.

Functional test execution can typically begin when the following preconditions hold:

The operational requirements to be tested have been specified and fully implemented.
The relevant software components have passed unit testing.
Software integration testing has started. However, initial functional testing can begin prior to the distribution of the software components onto the hardware components.
The relevant system components have passed system integration testing.
The independent test team is adequately staffed and trained in functional testing.
The test environment is ready.

Functional testing is typically complete when the following postconditions hold:

Functional testing typically involves the independent test team performing the following testing tasks using the following techniques:

Functional testing is typically performed on the following environments using the following tools:

Functional testing typically results in the production of all or part of the following work products from the test work product set:

Functional testing typically involves the following tasks being performed during the following phases:

PHASE → TASK ↓	Business Strategy (*)	Business Optimization	Initiation	Construction	Delivery	Usage	Retirement
Test Planning	Not Applicable	Not Applicable	Completed	Optional Regression	Not Applicable	Not Applicable	Not Applicable
Test Reuse	Not Applicable	Not Applicable	Optionally Started (**)	Completed	Not Applicable	Not Applicable	Not Applicable
Test Design	Not Applicable	Not Applicable	Optionally Started (**)	Completed	Not Applicable	Optional Regression	Not Applicable
Test Implementation	Not Applicable	Not Applicable	Optionally Started (**)	Completed	Not Applicable	Optional Regression	Not Applicable
Test Execution	Not Applicable	Not Applicable	Optionally Started (**)	Completed	Not Applicable	Optional Regression	Not Applicable
Test Reporting	Not Applicable	Not Applicable	Not Applicable	Completed	Not Applicable	Optional Regression	Not Applicable

(*) Optional functional testing of COTS software components during the technology analysis and technology vendor selection tasks.
(**) Optional functional testing of the executable architecture as well as the COTS components during the vendor and tool evaluation and vendor and tool selection tasks.

Functional testing is a requirements validation activity.
Functional testing is typically the most important type of system testing, and therefore usually involves the creation and execution of the most test suites of test cases.
The iterative and incremental development cycle implies that functional testing is regularly performed in an iterative and incremental manner.
Functional testing must be automated if adequate regression testing is to occur.
Functional testing can elicit failures produced by defects that are difficult to detect during launch testing.
Test cases for exceptional use case paths are part of robustness testing.
Multiple test cases per use case path may be appropriate to cover boundary value conditions.