This is a typical scenario of Manual Unit Testing activity-
A Unit is allocated to a Programmer for programming. Programmer has to use ‘Functional Specifications’ document as input for his work. Programmer prepares ‘Program Specifications’ for his Unit from the Functional Specifications. Program Specifications describe the programming approach, coding tips for the Unit’s coding.
Using these ‘Program specifications’ as input, Programmer prepares ‘Unit Test Cases’ document for that particular Unit. A ‘Unit Test Cases Checklist’ may be used to check the completeness of Unit Test Cases document.
‘Program Specifications’ and ‘Unit Test Cases’ are reviewed and approved by Quality Assurance Analyst or by peer programmer.
The programmer implements some functionality for the system to be developed. The same is tested by referring the unit test cases. While testing that functionality if any defects have been found, they are recorded using the defect logging tool whichever is applicable. The programmer fixes the bugs found and tests the same for any errors.
Stubs and Drivers
A software application is made up of a number of ‘Units’, where output of one ‘Unit’ goes as an ‘Input’ of another Unit. e.g. A ‘Sales Order Printing’ program takes a ‘Sales Order’ as an input, which is actually an output of ‘Sales Order Creation’ program.
Due to such interfaces, independent testing of a Unit becomes impossible. But that is what we want to do; we want to test a Unit in isolation! So here we use ‘Stub’ and ‘Driver.
A ‘Driver’ is a piece of software that drives (invokes) the Unit being tested. A driver creates necessary ‘Inputs’ required for the Unit and then invokes the Unit.
A Unit may reference another Unit in its logic. A ‘Stub’ takes place of such subordinate unit during the Unit Testing. A ‘Stub’ is a piece of software that works similar to a unit which is referenced by the Unit being tested, but it is much simpler that the actual unit. A Stub works as a ‘Stand-in’ for the subordinate unit and provides the minimum required behavior for that unit.
Programmer needs to create such ‘Drivers’ and ‘Stubs’ for carrying out Unit Testing.
Both the Driver and the Stub are kept at a minimum level of complexity, so that they do not induce any errors while testing the Unit in question.
Example - For Unit Testing of ‘Sales Order Printing’ program, a ‘Driver’ program will have the code which will create Sales Order records using hard coded data and then call ‘Sales Order Printing’ program. Suppose this printing program uses another unit which calculates Sales discounts by some complex calculations. Then call to this unit will be replaced by a ‘Stub’, which will simply return fix discount data.
