Probe effect is an unintended alteration in system behavior caused by measuring that system. In code profiling and performance measurements, the delays introduced by insertion or removal of code instrumentation may result in a non-functioning application, or unpredictable behavior.

Examples

In electronics, by attaching a

multimeter A multimeter is a measuring instrument that can measure multiple electrical properties. A typical multimeter can measure voltage, resistance, and current, in which case it is also known as a volt-ohm-milliammeter (VOM), as the unit is equipped w ...

, oscilloscope, or other testing device via a

test probe A test probe is a physical device used to connect electronic test equipment to a device under test (DUT). Test probes range from very simple, robust devices to complex probes that are sophisticated, expensive, and fragile. Specific types include t ...

, small amounts of

capacitance Capacitance is the capability of a material object or device to store electric charge. It is measured by the change in charge in response to a difference in electric potential, expressed as the ratio of those quantities. Commonly recognized a ...

, resistance, or

inductance Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current creates a magnetic field around the conductor. The field strength depends on the magnitude of t ...

may be introduced. Though good scopes have very slight effects, in sensitive circuitry these can lead to unexpected failures, or conversely, unexpected fixes to failures. In

debugging In computer programming and software development, debugging is the process of finding and resolving ''bugs'' (defects or problems that prevent correct operation) within computer programs, software, or systems. Debugging tactics can involve in ...

of parallel computer programs, sometimes failures (such as

deadlock In concurrent computing, deadlock is any situation in which no member of some group of entities can proceed because each waits for another member, including itself, to take action, such as sending a message or, more commonly, releasing a lo ...

s) are not present when the debugger's code (which was meant to help to find a reason for deadlocks by visualising points of interest in the program code) is attached to the program. This is because additional code changed the timing of the execution of parallel processes, and because of that deadlocks were avoided.Event manipulation for Nondeterministic Shared-Memory Programs
/ High-Performance Computing and Networking. 9th International Conference, HPCN Europe 2001, Amsterdam, The Netherlands, June 25–27, 2001, This type of bug is known colloquially as a

Heisenbug In computer programming jargon, a heisenbug is a software bug that seems to disappear or alter its behavior when one attempts to study it. The term is a pun on the name of Werner Heisenberg, the physicist who first asserted the observer effect ...

, by analogy with the observer effect in quantum mechanics.

Sources

{{DEFAULTSORT:Probe Effect Software testing Debugging