Reliability Testing GCSE Computing Starter Recap How do

Reliability & Testing GCSE Computing

Starter: Recap • How do you define a system? A system is a collection of parts that work together for a common purpose. It needs to receive and process inputs in order to produce outputs. • What is an “embedded system”? Software that is programmed to carry out a number of dedicated functions. For example, the software to run a washing machine is stored on a computer chip and embedded into the system.

Reliability Use of and reliance on computer systems • Computer systems are important and are involved in most human activities: – – – Safety Travel Business Entertainment Education Science • Given our dependence on them, it is vital we are able to trust in the reliability of these systems.

Reliability • IT failures can be catastrophic and expensive. • Air travel makes extensive use of computer systems. If these fail, then lives are put in danger: • On 7 th October 2008 an airbus operated by Quantas started to pitch violently because of a fault in an inertial reference sensor, causing the auto-pilot to try to correct suddenly. • Fortunately there were few major injuries on this occasion. • The problem was caused by faulty data sensors providing incorrect information to an automatic control system.

Reliability Use of and reliance on computer systems • Computer systems are important and are involved in most human activities: – – – Safety Travel Business Entertainment Education Science • Given our dependence on them, it is vital we are able to trust in the reliability of these systems.

Reliability Badly designed IT systems failing to achieve the desired result can cost millions or even billions of pounds that cannot be recovered. http: //www. information-age. com

TASK 7 minutes • Pick one of the previous sectors • Think about what problems would occur if systems used in that sector were unreliable • Add it to the following Padlet • http: //padlet. com/mrs_james/reliable Safety Travel Business Entertainment Education Science

Testing • Testing systems is a vital part of development and much time and effort is devoted to this • System testers are highly paid • Testing everything is impossible • Errors can slip through • Systems need to be monitored through their lives

What is testing? • Its not proving the system works – It might work in most cases but fail when unexpected data is input • Testing is carried out to purposely reveal errors – Testers try to break the system to reveal weaknesses • At the end, users test systems – Called “Beta testing” System is teste origina d again l specif st its ication. badly a If spec t the st ified a r t then di fix desi ffic gn flaw s at the ult to end

Task: Scenario 10 minutes • You are tasked to test a password checking system written by a pupil • The password should only be accepted if it is – 8 characters or longer – Contains at least 1 capital letter – Contains at least 1 number • What tests would you perform to check it worked as expected? – What passwords would you try? – What do you expect to happen in each case? Save Task do cument to H:

Types of test data • Suitable test data should cover the following situations: Valid Test data represents typical data input into the system Valid extreme Test data that is valid but at the extreme end of the range of acceptable input Invalid Test data that is out of range ad should be rejected Invalid extreme Test data that is invalid but only just Erroneous Test data that should be rejected because it is the wrong type of input