Prototype testing: This helps you at an early stage of 
development to find out whether a product meets 
requirements and user's expecttions. This is to find out 
design errors at an early stage when the functionalities 
are not yet implemented at or all or completely. Testing is 
done on the prototype of the product. The purpose of this 
is to identify particular areas of the UI that poses 
problem to the user and subsequently provide design 
solutins eliminating these problems.

Prototype is a roughly and rapidly developed model which is 
used for demonstrating to the custmor in order to gader 
clear requirements and also to win the confidence of the 
custmor. If we perform testing on this dummy model then it 
is called as prototype testing.