EEE 243B Applied Computer Programming

1. EEE 243BApplied Computer Programming Software engineering Life cycle and when to test

2. Review • What is the difference between white box and black box testing? • What does coverage give you? Maj JGA Beaulieu & Capt MWP LeSauvage

3. Outline • Software engineering (what is it?) • Basic software lifecycle • Verification and validation • Testing revisited Maj JGA Beaulieu & Capt MWP LeSauvage

4. Software engineering • Software engineering came of age as the demand on software products increased • The first few software programs were written by one person for his/her own purpose • These programs were small and were produced and used by experts • The flexibility afforded by software created a high demand and the number of projects and the size of the projects grew exponentially Maj JGA Beaulieu & Capt MWP LeSauvage

5. Software engineering • Software production was no longer an individual affair but became a team approach • As the teams grew bigger and the complexity of the software projects increased a requirement grew to better manage these projects • Some costly project delays, dropping quality of products and utter project failures in the late 1960s created what was called the software crisis Maj JGA Beaulieu & Capt MWP LeSauvage

6. Software engineering • Software engineering: Is a label that is normally applied to a set of current (best) practices for software development Shaw and Garland 1996 • Software engineering was first coined as an expression during a NATO conference in 1968 • The conference was created to address the problems brought on by the software crisis Maj JGA Beaulieu & Capt MWP LeSauvage

7. Software engineering • Engineering disciplines share five common traits: • Creating cost effective solutions – economical aspect • Solving practical problems – solutions that matter to the population (customer) • Apply scientific knowledge – science, math, analysis and design • Build things – tangible results • Work in the service of mankind – Not just a customer Maj JGA Beaulieu & Capt MWP LeSauvage

8. Basic software lifecycle • The quality of your software depends on all production activities: • Analysis – Will your program meet the needs of the user (client)? • Design – Is my design effective? Did I do a good decomposition and create a “readable” hierarchy of modules (high level) and functions (low level)? Did you chose the right design • Implementation – Is the code solid, efficient, well documented, complete? • Testing – Are my tests sufficient? • Maintenance – Did I introduce side effects during changes Maj JGA Beaulieu & Capt MWP LeSauvage

9. Basic software lifecycle • The 5 phases that we saw are often represented graphically as a waterfall; hence the waterfall model: Analysis Design Implementation Testing Maintenance Maj JGA Beaulieu & Capt MWP LeSauvage

10. Verification and Validation • There are parts of the testing that has nothing to do with the code!! …Really there is. • When you have elicited requirements as part of your analysis of the problem, you must test the requirements with your end user • This test is called Validation • Validation can occur at more than one stage of the software lifecycle Maj JGA Beaulieu & Capt MWP LeSauvage

11. Verification and Validation • When you finish your design, you must ensure that you took into account all the requirements from analysis. • So you test between these two phases • This extends to the entire lifecycle: • Every time you go from one phase to the next, you have to make sure you did not overlook anything, and • that each phase is complete and agrees with the results of the previous phase • This phase transition testing is called Verification Maj JGA Beaulieu & Capt MWP LeSauvage

12. Verification and Validation • Verification and validation (V&V) ensure that you catch potentials errors before you get to the code and testing of the code. • The reason for performing V&V at all stages of a project is to reduce the impact of changes later in the lifecycle • Correcting a mistake at the end of the project may require you to start back at the analysis stage! Maj JGA Beaulieu & Capt MWP LeSauvage

13. Verification and Validation • Verification ensures that each subsequent phase does not deviate from the requirement of the project • If a deviation from the project must occur for the product to work, then the verification process must identify and track this deviation • Verification ensures that the product is built to the right requirement - building the product right Maj JGA Beaulieu & Capt MWP LeSauvage

14. Verification and Validation • The first thing you try to do is to ensure that you have the requirement right • So validation has to do with building the right product • You may sometimes have to build a prototype or scaffolding in a software project to validate with the customer and get feedback Maj JGA Beaulieu & Capt MWP LeSauvage

15. Testing revisited • The scaffolding that you build as a prototype can also be used for testing purposes • In structured programming, we use a top-down approach to decompose our problems during the design phase • When we implement our design, we have two choices: • Bottom-up implementation • Top-down implementation Maj JGA Beaulieu & Capt MWP LeSauvage

16. Testing revisited • In bottom-up implementation, it may sometimes be necessary to provide input to or get output from a module or a function • In this case a driver can be used to simulate the input and get the output, as if the function under test was already part of a bigger system • Drivers in a scaffolding may only be a few lines of code, but they provide all the necessary environment needed by lower functions Maj JGA Beaulieu & Capt MWP LeSauvage

17. Testing revisited • In top-down implementation, it may be necessary for the upper modules or functions to obtain some results from lower functions • In this case, we can provide a stub in the scaffolding to generate the necessary data needed by the upper function Maj JGA Beaulieu & Capt MWP LeSauvage

18. Testing revisited • Many projects use both the top-down and the bottom-up approaches simultaneously. • In these cases the scaffolding may include both drivers and stubs • Stubs and drivers are small functions that form a scaffolding until the system is ready for integration • Integration testing may use scaffolding, to perform incremental testing as we integrate functions one at a time Maj JGA Beaulieu & Capt MWP LeSauvage

19. Testing revisited • Acceptance testing is the last phase of validation and is normally conducted in presence of the customer • Most large software producers also have a Quality Assurance department that can represent and assist the customer • For commercial software the QA department is the “customer” Maj JGA Beaulieu & Capt MWP LeSauvage

20. Quiz Time • What are the five phases of the software lifecycle? • What is the difference between verification and validation? • What is the difference between a driver and a stub? Maj JGA Beaulieu & Capt MWP LeSauvage