Entries Tagged 'Testing Interview questions' ↓

I have covered what is White box Testing in previous article. Here I will concentrate on Black box testing. BBT advantages, disadvantages and and How Black box testing is performed i.e the black box testing techniques.

Black box testing treats the system as a “black-box”, so it doesn’t explicitly use Knowledge of the internal structure or code. Or in other words the Test engineer need not know the internal working of the “Black box” or application.

Main focus in black box testing is on functionality of the system as a whole. The term ‘behavioral testing’ is also used for black box testing and white box testing is also sometimes called ‘structural testing’. Behavioral test design is slightly different from black-box test design because the use of internal knowledge isn’t strictly forbidden, but it’s still discouraged.

Each testing method has its own advantages and disadvantages. There are some bugs that cannot be found using only black box or only white box. Majority of the applicationa are tested by black box testing method. We need to cover majority of test cases so that most of the bugs will get discovered by blackbox testing.

Black box testing occurs throughout the software development and Testing life cycle i.e in Unit, Integration, System, Acceptance and regression testing stages.

Tools used for Black Box testing:
Black box testing tools are mainly record and playback tools. These tools are used for regression testing that to check whether new build has created any bug in previous working application functionality. These record and playback tools records test cases in the form of some scripts like TSL, VB script, Java script, Perl.

Advantages of Black Box Testing
- Tester can be non-technical.
- Used to verify contradictions in actual system and the specifications.
- Test cases can be designed as soon as the functional specifications are complete

Disadvantages of Black Box Testing
- The test inputs needs to be from large sample space.
- It is difficult to identify all possible inputs in limited testing time. So writing test cases is slow and difficult
- Chances of having unidentified paths during this testing

Methods of Black box Testing:

Graph Based Testing Methods:
Each and every application is build up of some objects. All such objects are identified and graph is prepared. From this object graph each object relationship is identified and test cases written accordingly to discover the errors.

Error Guessing:
This is purely based on previous experience and judgment of tester. Error Guessing is the art of guessing where errors can be hidden. For this technique there are no specific tools, writing the test cases that cover all the application paths.

Boundary Value Analysis:
Many systems have tendency to fail on boundary. So testing boundry values of application is important. Boundary Value Analysis (BVA) is a test Functional Testing technique where the extreme boundary values are chosen. Boundary values include maximum, minimum, just inside/outside boundaries, typical values, and error values.

Extends equivalence partitioning
Test both sides of each boundary
Look at output boundaries for test cases too
Test min, min-1, max, max+1, typical values

BVA techniques:
1. Number of variables
For n variables: BVA yields 4n + 1 test cases.
2. Kinds of ranges
Generalizing ranges depends on the nature or type of variables
Advantages of Boundary Value Analysis
1. Robustness Testing – Boundary Value Analysis plus values that go beyond the limits
2. Min – 1, Min, Min +1, Nom, Max -1, Max, Max +1
3. Forces attention to exception handling

Limitations of Boundary Value Analysis
Boundary value testing is efficient only for variables of fixed values i.e boundary.

Equivalence Partitioning:
Equivalence partitioning is a black box testing method that divides the input domain of a program into classes of data from which test cases can be derived.

How is this partitioning performed while testing:
1. If an input condition specifies a range, one valid and one two invalid classes are defined.
2. If an input condition requires a specific value, one valid and two invalid equivalence classes are defined.
3. If an input condition specifies a member of a set, one valid and one invalid equivalence class is defined.
4. If an input condition is Boolean, one valid and one invalid class is defined.

Comparison Testing:
Different independent versions of same software are used to compare to each other for testing in this method.

Reference- http://www.softrel.org/stgb.html

What is White Box Testing?
White box testing (WBT) is also called Structural or Glass box testing.

White box testing involves looking at the structure of the code. When you know the internal structure of a product, tests can be conducted to ensure that the internal operations performed according to the specification. And all internal components have been adequately exercised.

White Box Testing is coverage of the specification in the code.

Code coverage:

Segment coverage:
Ensure that each code statement is executed once.

Branch Coverage or Node Testing:
Coverage of each code branch in from all possible was.

Compound Condition Coverage:
For multiple condition test each condition with multiple paths and combination of different path to reach that condition.

Basis Path Testing:
Each independent path in the code is taken for testing.

Data Flow Testing (DFT):
In this approach you track the specific variables through each possible calculation, thus defining the set of intermediate paths through the code.DFT tends to reflect dependencies but it is mainly through sequences of data manipulation. In short each data variable is tracked and its use is verified.
This approach tends to uncover bugs like variables used but not initialize, or declared but not used, and so on.

Path Testing:
Path testing is where all possible paths through the code are defined and covered. Its a time consuming task.

Loop Testing:
These strategies relate to testing single loops, concatenated loops, and nested loops. Independent and dependent code loops and values are tested by this approach.

Why we do White Box Testing?
To ensure:

• That all independent paths within a module have been exercised at least once.
• All logical decisions verified on their true and false values.
• All loops executed at their boundaries and within their operational bounds internal data structures validity.

Need of White Box Testing?
To discover the following types of bugs:

• Logical error tend to creep into our work when we design and implement functions, conditions or controls that are out of the program
• The design errors due to difference between logical flow of the program and the actual implementation
• Typographical errors and syntax checking

Skills Required:
We need to write test cases that ensure the complete coverage of the program logic.
For this we need to know the program well i.e. We should know the specification and the code to be tested. Knowledge of programming languages and logic.

Limitations of WBT:
Not possible for testing each and every path of the loops in program. This means exhaustive testing is impossible for large systems.
This does not mean that WBT is not effective. By selecting important logical paths and data structure for testing is practically possible and effective.
Reference- http://www.softrel.org/stgb.html

Comment out your queries on white box testing below. Meantime I will cover Black box testing in detail.

Software Testing Types:

Black box testing – Internal system design is not considered in this type of testing. Tests are based on requirements and functionality.

White box testing – This testing is based on knowledge of the internal logic of an application’s code. Also known as Glass box Testing. Internal software and code working should be known for this type of testing. Tests are based on coverage of code statements, branches, paths, conditions.

Unit testing – Testing of individual software components or modules. Typically done by the programmer and not by testers, as it requires detailed knowledge of the internal program design and code. may require developing test driver modules or test harnesses.

Incremental integration testing – Bottom up approach for testing i.e continuous testing of an application as new functionality is added; Application functionality and modules should be independent enough to test separately. done by programmers or by testers.

Integration testing – Testing of integrated modules to verify combined functionality after integration. Modules are typically code modules, individual applications, client and server applications on a network, etc. This type of testing is especially relevant to client/server and distributed systems.

Functional testing – This type of testing ignores the internal parts and focus on the output is as per requirement or not. Black-box type testing geared to functional requirements of an application.

System testing – Entire system is tested as per the requirements. Black-box type testing that is based on overall requirements specifications, covers all combined parts of a system.

End-to-end testing – Similar to system testing, involves testing of a complete application environment in a situation that mimics real-world use, such as interacting with a database, using network communications, or interacting with other hardware, applications, or systems if appropriate.

Sanity testing - Testing to determine if a new software version is performing well enough to accept it for a major testing effort. If application is crashing for initial use then system is not stable enough for further testing and build or application is assigned to fix.

Regression testing – Testing the application as a whole for the modification in any module or functionality. Difficult to cover all the system in regression testing so typically automation tools are used for these testing types.

Acceptance testing -Normally this type of testing is done to verify if system meets the customer specified requirements. User or customer do this testing to determine whether to accept application.

Load testing – Its a performance testing to check system behavior under load. Testing an application under heavy loads, such as testing of a web site under a range of loads to determine at what point the system’s response time degrades or fails.

Stress testing – System is stressed beyond its specifications to check how and when it fails. Performed under heavy load like putting large number beyond storage capacity, complex database queries, continuous input to system or database load.

Performance testing – Term often used interchangeably with ‘stress’ and ‘load’ testing. To check whether system meets performance requirements. Used different performance and load tools to do this.

Usability testing – User-friendliness check. Application flow is tested, Can new user understand the application easily, Proper help documented whenever user stuck at any point. Basically system navigation is checked in this testing.

Install/uninstall testing - Tested for full, partial, or upgrade install/uninstall processes on different operating systems under different hardware, software environment.

Recovery testing – Testing how well a system recovers from crashes, hardware failures, or other catastrophic problems.

Security testing – Can system be penetrated by any hacking way. Testing how well the system protects against unauthorized internal or external access. Checked if system, database is safe from external attacks.

Compatibility testing – Testing how well software performs in a particular hardware/software/operating system/network environment and different combination s of above.

Comparison testing – Comparison of product strengths and weaknesses with previous versions or other similar products.

Alpha testing – In house virtual user environment can be created for this type of testing. Testing is done at the end of development. Still minor design changes may be made as a result of such testing.

Beta testing – Testing typically done by end-users or others. Final testing before releasing application for commercial purpose.

Happy Testing!!!

If you like this post you may want to subscribe to our email newsletter to get latest updates on software testing!! It’s 100% free!!

Do not forget to confirm your subscription request by logging into your Email inbox.

In recent days this is the most asked question to me by readers. How to get software testing job? How to come in software testing field? or Can I get job in testing?

All these questions are similar and I want to give also similar answer for this. I have written post on choosing software testing as your career where you can analyze your abilities and know which are the most important skills required for software testing.

Continue reading →

In this post I am gonna give answer to reader’s question.
There was one question asked by Srividya:
Q.What is difference between client server and Web Testing?
Vijay: Well Srividya I would like to add one more testing type i.e Desktop Testing in this discussion. So now we have three testing types Desktop application testing, Client server application testing and Web application testing.

Each one differs in the environment in which they are tested and you will lose control over the environment in which application you are testing, while you move from desktop to web applications.

Desktop application runs on personal computers and work stations, so when you test the desktop application you are focusing on a specific environment. You will test complete application broadly in categories like GUI, functionality, Load, and backend i.e DB.

In client server application you have two different components to test. Application is loaded on server machine while the application exe on every client machine. You will test broadly in categories like, GUI on both sides, functionality, Load, client-server interaction, backend. This environment is mostly used in Intranet networks. You are aware of number of clients and servers and their locations in the test scenario.

Web application is a bit different and complex to test as tester don’t have that much control over the application. Application is loaded on the server whose location may or may not be known and no exe is installed on the client machine, you have to test it on different web browsers. Web applications are supposed to be tested on different browsers and OS platforms so broadly Web application is tested mainly for browser compatibility and operating system compatibility, error handling, static pages, backend testing and load testing.

I think this will have an idea of all three testing environment. Keep in mind that even the difference exist in these three environment, the basic quality assurance and testing principles remains same and applies to all.

In this post I am going to answer some of the questions asked by one of the reader Srinivas M.

1. In an application currently in production, one module of code is being modified. Is it necessary to re-test the whole application or is it enough to just test functionality associated with that module?

Vijay: Well, the answer is both. You will have to test the functionality of that module as well as the other modules. But you can differentiate on the stress to be given on the module to be tested.

I think this scenario will explain the answer to your question well.

If Module A is modified, Module B is depending on module A, and Module C is a general module independent of module A.
So in this case you will test the module A in depth to all test cases. Then your next stress will be on module B. Wait now what about module C? You will have to test this module as well but may be with less stress because module C is not depend on module A but may be depend on module B.

Again if you are a white box tester you probably know which modules will get affected and which modules should be tested. But as a black box tester you will need to do regression testing as well.

2. What is the most challenging situation you had during testing?

Vijay: A good question! When I switched my job some years back I was being asked the same question.
Well a good answer to this question is depends on each ones experience. If you came across any such a situation and found any interesting Bug that was difficult to find out or analyzed any project risk accurately before occurring then this could be the answer to this question.

Keep in mind that when answering such a question, be realistic and don’t overstress the situation.

3. What are you going to do if there is no Functional Spec or any documents related to the system and developer who wrote the code does not work in the company anymore, but you have system and need to test?

Vijay: A typical situation in Indian companies! Right? Due to high attrition rate
In this case fist you will need to do the exploratory testing of the product. In this testing you will come to know the system and its basic workflow. In exploratory testing you can also find some ‘blocker’ bugs that cause system to be crash.

If you are a white box tester then next step you can do is to see the different module code. By this you will know the test cases for different modules and relation of modules.

If you have any question please comment it below.