Lua Programming/Appendix:Software testing

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The term software testing refers to a number of methods and processes that are used to discover bugs and programming mistakes in computer software. Software testing can be done statically, in which case in is called static testing and is done without executing the computer software, or dynamically, in which case it is called dynamic testing and is done while the computer program that is being tested is running.

Type checking[edit]

In programming languages, a type system is a collection of rules that assign a property called a type to the various constructs—such as variables, expressions, functions or modules—a computer program is composed of. The main purpose of a type system is to reduce bugs in computer programs by defining interfaces between different parts of a computer program, and then checking that the parts have been connected in a consistent way. This checking can happen statically (at compile time), dynamically (at run time), or it can happen as a combination of static and dynamic checking. Type systems have other purposes as well, such as enabling certain compiler optimizations, allowing for multiple dispatch, providing a form of documentation, etc.
—Wikipedia, Type system

Type-checking can be done, as the extract from Wikipedia brilliantly said, at run time or at compile time. If it is done at compile time, the compiler, when compiling source code, will verify the type safety of the program and guarantee that the program satisfies certain type safety properties—generally, static type-checkers will simply verify that variables always have values of the same type and that arguments passed to functions will have the right type.

The static approach allows bugs to be discovered early in the development cycle. The dynamic approach, in contrast, consists in verifying that the program follows the type constraints when it is running. While this means that dynamic type-checkers should be able to verify more constraints, most dynamically typed languages do not have many type constraints. Lua is a dynamically typed language: in Lua, values have types, but variables do not. This means that the value of a variable can be a number at some point of the program’s execution and be a string at another point.

Lua’s type system is very simple in comparison with most other languages. It performs type checking when operators are used (attempting to add two values of which at least one is not a number and cannot be coerced to one, for example, will raise a type error) and when functions of the standard libraries are called (functions of the standard library reject arguments that do not have the right type and raise an appropriate error).

Further reading[edit]

The lua-users wiki, an excellent resource to find information about Lua, provides the following material that is related to software testing. Some of these pages consist in links to other pages or to projects that can be useful for various tasks.