black box testing techniques based on external 
specification without of how the system is constructed.

 black box Testing Strategies/Techniques

1. black box testing should make use of randomly generated 
inputs (only a test range should be specified by the 
tester), to eliminate any guess work by the tester as to 
the methods of the function  
2. data outside of the specified input range should be 
tested to check the robustness of  the program  
3. boundary cases should be tested (top and bottom of 
specified range) to make sure the highest and lowest 
allowable inputs produce proper output 
4. the number zero should be tested when numerical data is 
to be input 
4.stress testing should be performed (try to overload the 
program with inputs to see where it reaches its maximum 
capacity), especially with real time systems 
5. crash testing should be performed to see what it takes 
to bring the system down 
6. test monitoring tools should be used whenever possible 
to track which tests have already been performed and the 
outputs of these tests to avoid repetition and to aid in 
the software maintenance 
7. other functional testing techniques include: transaction 
testing, syntax testing, domain testing, logic testing, and 
state testing. 
8.finite state machine models can be used as a guide to 
design functional tests

The Black Box techniques are
1.Boundary Value Analysis(BVA)
2.Eqivalence class partitions(ECP)
3.Decision Table(DT) and 
4.State Transition Diagram(STD)

B.V.A (Boundary Value Analysis)

E.C.P( Equallence Class Partition)

Error Guessing

Black Box Design Techniques :

1. B.V.A(Boundary Value Analisys)

Input values of the boundaries of input domain are tested.

Example :
An inventory raises from 10,000 unit to 20,000 unit.
If A is valid boundary of 10,000 and B is valid boundary of 
20,000 then invalid boundary of A is A-1 and same for B is 
B-1.

Then Valid Boundary values are : 10,000(A) and 20,000(B)
and Invalid Bounadry values are 9,999(A-1) and 19,999(B-1).

Advantages :
i)Small set of inputs
ii)Very clear guideline for choosing inputs

Disadvantages :
i)Doesn't combine all possible set of inputs.

2. E.C.P(Equivalence Class Partitioning)

Same types of inputs will be placed in same class;

Example:
For above example 
Valid Class for A & B
Invalid Class for A-1 & B-1

Advantages :
i)Minimizes set of inputs
Disadvantages :
i) No guide line for choosing inputs
ii)Doesn't combine all possible inputs

Error Guessing

An informal technique where experienced tester apply his or 
her logic to find out defects after when a lot of formal 
techniques have applied already.