What is black box testing and White box testing?

Black box testing is also termed as functional testing. It ignores how the internal

functionality of a system works and depends only what are the outputs on specified

inputs. Source code availability is not an important in back box testing. Black box testing

is mostly to ensure that it meets the user functionality.

According to IEEE standards following are characteristics of Black box testing:-

“Testing that ignores the internal mechanism of a system or component and focuses

solely on the outputs generated in response to selected inputs and execution



“Testing conducted to evaluate the compliance of a system or component with

specified functional requirements.”

One of the ways of black box testing is Manual testing what the tester performs. For

instance you can install the application on a machine and tester starts testing is a type of

black box testing. In this case the tester is completely unaware of the how the program

logic flows and how its coded etc.

White box testing is opposite to Black box it requires internal know how of how the logic

flows. As this testing needs know how of the internal structure it can only be done

programmers. Unit testing is one of the ways of doing White box testing in which

programmers use NUNIT or JNUIT to test each class individually. White box testing can

be done by programmer by either stepping through the code or testing the classes and

components in isolation.

(B) What’s the difference between Unit testing, Assembly

testing and Regression testing?

Unit testing is also called as Component testing. Unit testing ensures that reliable program

unit meets their requirements. Unit testing is normally conducted by programmer under

the supervision of the project lead or the team Lead. Main objective of this testing is to

test each unit in isolation and individually. This is done by knowing what are the inputs to

the unit and what the expected outputs for the same. Unit testing is a white box activity.

Unit test normally comes in the implementation phase of the project.

For instance in the below figure we are trying to do unit testing on the customer class. So

we create the object of Customer class assign “CustomerCode” and “Age” property and

check for the response. For instance in this condition we tried to pass a non-numeric

value to the “Age” property and the class threw an error saying “Age should be numeric”.

So here the basic unit testing entity is your class.


Figure 12.6 : – Unit testing for sample Customer class

But unit testing is not limited to a component, object or function. So definition of a unit

testing will depend on the approach. Below are some examples of unit testing:-

Check points in UI like tab orders, error messages, look and feel etc.

Class, object, component level testing as said previously.

In case of functional programming can be a simple method or function.

Logic testing for algorithms. Some projects can have some critical algorithm for

instance some kind of custom sorting, security implementation etc. So that logic

can be tested independently.

But the general thumb rule of what is Unit in Unit testing is that the module self contained

and by itself.

Assembly testing goes one step ahead than unit testing. It demonstrates that can the

modules interact in a correct, stable and proper manner as defined by the functional

specifications provided by the client. Assembly testing is Black box testing style and also

called as Integration testing. For instance in the above unit test of the “Customer” class,

testing was done in isolation. But in actually the “Customer” class is not going to be stand

alone rather it will be used more in conjunction with the “Product” class and also will

have UI to do the same. So in short the “Customer” class will work with two more entity


one is the “UI” and the other is the “Product” class. So normally assembly testing is done

through UI but not necessarily.

Figure 12.7 : – Integration Testing

The above figure defines a simple scenario for integration testing. The same “Customer”

class is now tested with the “UI” and “Product” to see if the interaction between them

matches according to functional specifications.

Regression testing ensures that application function properly even if there are changes or

enhancements to system.For instance you change the “Product” class still you will run all

the test cases for “Product” , “Customer” and “UI” just to make sure that any changes in

“Product” class does not affect interaction with other entities. So you will see when

testers do a regression testing they run all the scripts to ensure that nothing has been


(I)What is V model in testing?

V model map’s the type of test to the stage of development in a project.


Figure 12.8 : – V Model

Unit Testing

Starting from the bottom the first test level is “Unit Testing”. It involves checking that

each feature specified in the “Component Design” has been implemented in the


In theory an independent tester should do this, but in practice the developer usually does

it, as they are the only people who understand how a component works. The problem

with a component is that it performs only a small part of the functionality of a system,

and it relies on co-operating with other parts of the system, which may not have been

built yet. To overcome this, the developer either builds, or uses special software to trick

the component into believe it is working in a fully functional system.

Integration Testing

As the components are constructed and tested they are then linked together to check if

they work with each other. It is a fact that two components that have passed all their


tests, when connected to each other produce one new component full of faults. These

tests can be done by specialists, or by the developers.

Integration Testing is not focused on what the components are doing but on how they

communicate with each other, as specified in the “System Design”. The “System Design”

defines relationships between components.

The tests are organized to check all the interfaces, until all the components have been

built and interfaced to each other producing the whole system.

System Testing

Once the entire system has been built then it has to be tested against the “System

Specification” to check if it delivers the features required. It is still developer focused,

although specialist developers known as systems testers are normally employed to do it.

In essence System Testing is not about checking the individual parts of the design, but

about checking the system as a whole. In fact it is one giant component.

System testing can involve a number of specialist types of test to see if all the functional

and non-functional requirements have been met. In addition to functional requirements

these may include the following types of testing for the non-functional requirements:

Performance – Are the performance criteria met?

Volume – Can large volumes of information be handled?

Stress – Can peak volumes of information be handled?

Documentation – Is the documentation usable for the system?

Robustness – Does the system remain stable under adverse circumstances?

There are many others, the need for which is dictated by how the system is supposed to


Acceptance Testing

Acceptance Testing checks the system against the “Requirements”. It is similar to systems

testing in that the whole system is checked but the important difference is the change in



Systems testing checks that the system that was specified has been delivered. Acceptance

Testing checks that the system will deliver what was requested.

The customer should always do acceptance testing and not the developer . The customer

knows what is required from the system to achieve value in the business and is the only

person qualified to make that judgment. This testing is more of getting the answer for

whether is the software delivered as defined by the customer. It’s like getting a green flag

from the customer that the software is up to the expectation and ready to be used.


2 Responses to “Testing?”

  1. Rickson Says:

    So professional, I hope you had written pages and pages of your experiences. I have a testing interview tomorrow.

  2. developers Says:

    Who can offer a good source of ready tab bar icons for my iOS apps?
    I make an apps for medicine fo iPhone

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