Incremental Testing

Incremental Testing means that you test two related programs together and make sure they are working correctly. Then you add one or two additional modules to the test until all of the components are successfully working together.

This is usually the best approach for large, complex systems. (The alternative approach is called Big Bang, where you wait and test the entire system all at one time.)

Incremental Testing requires the creation of stub and driver programs. These are shell programs that do nothing but allow programs to make calls to other modules and databases.

A stub program is one that is called by the program you are testing and a driver program is one that calls your program.

As an example, say you have Program A that calls a second Program B. However, Program B is not ready to include in your testing. So, you create a stub Program B that does nothing but accept your input parameters and display the fields.

This allows you to test Program A now and at least ensure that it is passing the correct data to Program B. Likewise, let us say you are testing Program B, but the calling Program A is not ready.

In this case, you can create a driver Program A that has no logic other than to pass a predefined table of parameter input to Program B. Program B then accepts the data and performs the expected logic.

If you perform an incremental integration test, there are two general ways to put the component modules together - top down and bottom up.

These two approaches are available if your solution follows a general high-level to low-level hierarchy - that is, you have general programs that call other programs for detailed processing, which, in turn, call other programs for even more detailed logic processing.

  • Top Down. In this approach, the modules at the top of the overall logic path are tested first, using stubs for the called modules. Then the called modules are added, using stubs for modules that they might call. This continues until the entire application is tested. This can be easier to logically understand, but it saves the bulk of the testing complexity until later.
  • Bottom Up. This is the opposite. You first start off with programs at the lower level, and utilize driver programs to call them. Then you replace the drivers with the actual programs and create driver programs to call them from one level up. This continues until all the programs are tested and in place. The bottom up approach tests the bulk of the processing logic earlier, but it is harder to see the bigger picture until later, when the more general programs are in place.

In general, incremental testing is better for large, complex systems. The integration testing process can start earlier, as soon as related programs have been successfully unit tested.

This approach makes it easier to find errors, since the application environment only introduces one (or a few) module at a time. Lastly, this approach results in more overall testing, since the earlier modules get tested over and over again as new modules are added.

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Libro El Director de Proyectos Práctico -

Un Método probado de 28 Pasos para completar tu Proyecto Exitosamente


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El Director de Proyectos Práctico, Project Management for Small Projects. 

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