A dry run is a testing process where the effects of a possible failure are intentionally mitigated. For example, an aerospace company may conduct a "dry run" test of a jet's new pilot ejection seat while the jet is parked on the ground, rather than while it is in flight.

In computer programming

Computer programming

Computer programming is the process of designing, writing, testing, debugging, and maintaining the source code of computer programs. This source code is written in one or more programming languages. The purpose of programming is to create a program that performs specific operations or exhibits a...

, a dry run is a mental run of a computer program

Computer program

A computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...

, where the computer programmer examines the source code

Source code

In computer science, source code is text written using the format and syntax of the programming language that it is being written in. Such a language is specially designed to facilitate the work of computer programmers, who specify the actions to be performed by a computer mostly by writing source...

 one step at a time and determines what it will do when run. In theoretical computer science

Computer science

Computer science or computing science is the study of the theoretical foundations of information and computation and of practical techniques for their implementation and application in computer systems...

, a dry run is a mental run of an algorithm

Algorithm

In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...

, sometimes expressed in pseudocode

Pseudocode

In computer science and numerical computation, pseudocode is a compact and informal high-level description of the operating principle of a computer program or other algorithm. It uses the structural conventions of a programming language, but is intended for human reading rather than machine reading...

, where the computer scientist

Computer scientist

A computer scientist is a scientist who has acquired knowledge of computer science, the study of the theoretical foundations of information and computation and their application in computer systems....

 examines the algorithm's procedures one step at a time. In both uses, the dry run is frequently assisted by a table (on a computer screen or on paper) with the program or algorithm's variables

Variable (programming)

In computer programming, a variable is a symbolic name given to some known or unknown quantity or information, for the purpose of allowing the name to be used independently of the information it represents...

 on the top.

The usage of "dry run" in acceptance procedures (for example in the so called FAT = factory acceptance testing) is meant as following: the factory - which is a subcontractor - must perform a complete test of the system it has to deliver before the actual acceptance from the contractor side.