BLACK BOX TESTING

It is verifying the functionality ( behavior ) against requirement specifications.

Types of Black Box Testing

1) FUNCTIONAL TESTING

Also called component testing. Testing each and every component thoroughly (rigorously) against requirement specifications is known as functional testing.

For ex, let us consider that Citibank wants a s/w for banking purpose and it asks the company Iflex to develop this s/w. The s/w is something as shown below. When the user clicks his valid user name and enters his password, then he is taken into the homepage. Once inside the homepage, he clicks on amount transfer and the below page is displayed. He enters his valid account number and then the account number to which the money is to be transferred. He then enters the necessary amount and clicks on transfer. The amount must be transferred to the other account number.

Now in black box testing, the test engineer tests the s/w against requirements and checks if the s/w is working correctly as per requirements. 

This is how the requirements given by the client looks like (figure below). It is usually a word document file. Let us consider that Citibank gives a 80pg SRS in MS-WORD format. The test engineer then looks at the requirements and correspondingly checks the s/w.

Now the test engineer does all possible tests on the 2 account numbers. Now, he proceeds with the testing of Amount transfer. These are the following tests he conducts for testing the amount field,

He enters the following data in the amount field,

a) – 100           X                      b) 100$                        X                      c)100.50          X

d) Hundred rupees only        X          e) 100 blank space 0               X

f) 100                           g)0.001                        X

For all the above cases except for f) , it should throw an error message. If it doesn’t throw, then there is a bug in the s/w and the s/w must be sent to the development team to repair the defect.

Thus, during testing, we must remember the following points,

a) We must always start testing the application with the valid data. In the above example for amount transfer, we see that we have entered the valid data 100 only in the 6^th test. This should not be done, because if the valid data itself is not taken correctly, then we need not have to waste our time checking for the invalid data

b) If the application works for valid data, only then we must start testing for invalid data

c) If the application is not working for 1 of the invalid values, then we can continue testing for all the other invalid values and then submit the test report of all the defects for invalid values.

d) In testing, we should not assume or propose requirement. If we have any queries, talk to the one who knows the requirements very well and clarify the queries.

e) We must not do over-testing ( testing for all possible junk values ) or under-testing ( testing for only 1 or 2 values ). We must only try and do optimize testing (testing for only the necessary values- both invalid and valid data).

f) We must do both positive testing (testing for valid data) and negative testing (testing for invalid data).

The characterstics of a good requirement are,

1) Unitary ( cohesive ) – the requirement addresses 1 and only 1 thing

2) Complete – the requirement is fully stated in 1 place with no missing information

3) Consistent – the requirement does not contradict any other requirement and is fully consistent with all authoritative external documentation

4) Non-Conjugated ( Atomic ) – the requirement is atomic i.e, it does not contain certain conjunctions. Ex – “the postal code field must validate American and Canadian postal codes” should be written as two separate requirements : 1) “The postal code field must validate American Postal codes” and 2) “The postal code field must validate Canadian Postal codes”.

5) Traceable – the requirement meets all or part of a business need as stated by stakeholders and authoritatively documented

6) Current – the requirement has not been made obsolete by the passage of time

7) Unambiguous – the requirement is concisely stated without recourse to technical jargon, acronyms etc. it expresses objective facts, not subjective opinions. It is subjective to one and only one interpretation.

8) Mandatory – the requirement represents a stakeholder defined characterstic the absence of which will result in a deficiency that cannot be ameliorated

9) Verifiable – the implementation of the requirement can be determined through one of 4 possible methods – inspection, demonstration, test or analysis.