CS636 Slides

Software Errors ·  Increased size and complexity leads to software errors ·  Error: software does not provide the intended behavior ·  Errors lead to failure

 Cost

 High relieability software cannot tolerate errors

 Incorrect specifications OR Specification were not followed (misinterpreted)  Specifications are important for error free software A typical UML diagram for the BankAccount class *

* Formal Software Development, from VDB to Java by Quentin Charatan and Aaron Kans Withdraw: Receives a requested amount to withdraw from the bank account and, if there are sufficient funds in the account, meets the request. Returns a boolean value indicating success or failure of the attempt to withdraw money from the account.

• Is it that the bank account must contain at least the amount of money that Is requested for withdrawal?

• Or is there a minimum balance that must be maintained?

• Or is there an agreed overdraft limit?

UML notation

Software Testing

 Testing aims to locate the errors

 Testing cannot take place until some implementation is available

 Correcting errors identified by testing may introduce new errors

 Testing can uncover errors, does not guarantee absence of them

 Testing is based on specifications, ambiguous specifications may make testing ineffective