Severity vs Priority.

Severity & Priority in Software Testing :-
There are Two things in bugs/defects of the software testing:-
Severity :- Severity tells the seriousness of a bug on the product functionality. It is assigned by Tester based on seriousness of the bug. We have got four different levels for Severity. Tester sets the severity of bug.
Severity can be categorized into following levels
1. Critical/S1 :- A defect that completely affects or hampers testing of an application/functionality is called a critical or S1 defect.
2. Major/S2 :- In S2 or Major level, Major functionality of an application doesn't work but tester can test the application.
3. Moderate/S3 :- In Moderate or S3 level, Its causing few undesirable behavior, however system or an application is still usable to a high degree.
4. Low/Cosmetic/S4 :- In Cosmetic level, only the changes are related to UI i.e. look and feel of the application. Such defect or bugs doesn't harm the application under test.

Priority :- Priority defines the order. Which bug should rectify first? Should we fix it now or later? Developer or a Project Manager decides the priority of bug.
Priority can be categorized into following levels (P1 as highest and P4 as lowest):
Urgent (P1):- Must be fixed in the next built.
High(P2):- Must be fixed in any of the upcoming builts but should be included in the release.
Medium(P3):- May be fixed after the release.
Low(P4):- May or may not be fixed at all.


Lets take the examples of Priority and Severity :-
1. High Priority and High Severity :- If a valid user goes to login panel (when it is already member) and gives valid credentials to the required fields. And system throws an error like invalid credential. It is comes under High Priority and High Severity. Therefore this bug needs to be fixed as early as possible.
 
2. High Priority and Low Severity :- Lets take an example of Flipkart.com. Suppose while updating Flipkart.com, they updated the wrong logo accidentally with spell missing like Flipart.com, here "k" is missing. It should be Flipkart.com. Now here bug is High Priority and Low Severity bug because this bug is High Priroty, therefore Flipkart has to resolve this problem to keep its brand value.
 
3. Low Priority and Low Severity :- Lets talk about well known and well used shopping website portal Flipkart.com. Everyone knows logo of Flipkart.com. Suppose while updating the website they made a spelling mistake in the content or somewhere in home page. Its fine it wont impact much. User can still use the website. This kind of bug comes under Low Priority and Low Severity. It is also called cosmetic error.
 
4. High Severity and Low Priority :- Lets take an example of an application, while using the application, if that application crashes after multiple use of functionality like: after clicking 200 clicks on save button and suddenly application gets corrupted. So such kind of bug comes under High Severity and Low Priority.

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What is Stubs & Drivers? Why We Use Stubs And Drivers? Describe with an example.

What is Stubs and Drivers. Why do we use them?
Stubs:- Stubs are simply a dummy modules, that are always recognize as "called program" or in simple, stubs are used in integration testing (top-down approach).
Stubs are generally used when sub programs are under construction.
Example:- Let us take an example of an application, where we have 3 modules ie. Login, Home and user modules. Now Login module is ready and need to go under test, so for that we need to call functions from home and user (which are not completed). Therefore, to test those modules or functions we need to write a short dummy piece of code for home and user. So that it simulates home and user, which will return any values for Login. This short dummy piece of code is called Stubs.

Drivers:- Drivers are also considered as dummy modules, that are distinguish as "calling program" that is used in bottom up integration testing.
Drivers are only used when main program are under construction.
Example:- Considering the same Example as above: When we have Home and User modules get ready and Login module is not, and we need to test Home and User modules, which return values from Login module, So to extract the values from Login module, we write a Short Piece of Dummy code for login which returns value for home and user, So these pieces of code is always called Drivers.

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Some Major Computer System Failures caused by Software Bugs earlier.

In March of 2002 it was reported that software bugs in Britain's national tax system resulted in more than 100,000 erroneous tax overcharges. The problem was partly attributed to the difficulty of testing the integration of multiple systems.

1· A newspaper columnist reported in July 2001 that a serious flaw was found in off-the-shelf software that had long been used in systems for tracking certain U.S. nuclear materials. The same software had been recently donated to another country to be used in tracking their own nuclear materials, and it was not until scientists in that country discovered the problem, and shared the information, that U.S. officials became aware of the problems.

2· According to newspaper stories in mid-2001, a major systems development contractor was fired and sued over problems with a large retirement plan management system. According to the reports, the client claimed that system deliveries were late, the software had excessive defects, and it caused other systems to crash.

3· In January of 2001 newspapers reported that a major European railroad was hit by the aftereffects of the Y2K bug. The company found that many of their newer trains would not run due to their inability to recognize the date '31/12/2000'; the trains were started by altering the control system's date settings.

4· News reports in September of 2000 told of a software vendor settling a lawsuit with a large mortgage lender; the vendor had reportedly delivered an online mortgage processing system that did not meet specifications, was delivered late, and didn't work.

5· In early 2000, major problems were reported with a new computer system in a large suburban U.S. public school district with 100,000+ students; problems included 10,000 erroneous report cards and students left stranded by failed class registration systems; the district's CIO was fired. The school district decided to reinstate it's original 25-year old system for at least a year until the bugs were worked out of the new system by the software vendors.

6· In October of 1999 the $125 million NASA Mars Climate Orbiter spacecraft was believed to be lost in space due to a simple data conversion error. It was determined that spacecraft software used certain data in English units that should have been in metric units. Among other tasks, the orbiter was to serve as a communications relay for the Mars Polar Lander mission, which failed for unknown reasons in December 1999. Several investigating panels were convened to determine the process failures that allowed the error to go undetected.

7· Bugs in software supporting a large commercial high-speed data network affected 70,000 business customers over a period of 8 days in August of 1999. Among those affected was the electronic trading system of the largest U.S. futures exchange, which was shut down for most of a week as a result of the outages.

8· In April of 1999 a software bug caused the failure of a $1.2 billion military satellite launch, the costliest unmanned accident in the history of Cape Canaveral launches. The failure was the latest in a string of launch failures, triggering a complete military and industry review of U.S. space launch programs, including software integration and testing processes. Congressional oversight hearings were requested.

9· A small town in Illinois received an unusually large monthly electric bill of $7 million in March of 1999. This was about 700 times larger than its normal bill. It turned out to be due to bugs in new software that had been purchased by the local power company to deal with Y2K software issues.

10· In early 1999 a major computer game company recalled all copies of a popular new product due to software problems. The company made a public apology for releasing a product before it was ready.

· The computer system of a major online U.S. stock trading service failed during trading hours several times over a period of days in February of 1999 according to nationwide news reports. The problem was reportedly due to bugs in a software upgrade intended to speed online trade confirmations.

11· In April of 1998 a major U.S. data communications network failed for 24 hours, crippling a large part of some U.S. credit card transaction authorization systems as well as other large U.S. bank, retail, and government data systems. The cause was eventually traced to a software bug.

12· January 1998 news reports told of software problems at a major U.S. telecommunications company that resulted in no charges for long distance calls for a month for 400,000 customers. The problem went undetected until customers called up with questions about their bills.

13· In November of 1997 the stock of a major health industry company dropped 60% due to reports of failures in computer billing systems, problems with a large database conversion, and inadequate software testing. It was reported that more than $100,000,000 in receivables had to be written off and that multi-million dollar fines were levied on the company by government agencies.

14· A retail store chain filed suit in August of 1997 against a transaction processing system vendor (not a credit card company) due to the software's inability to handle credit cards with year 2000 expiration dates.

15· In August of 1997 one of the leading consumer credit reporting companies reportedly shut down their new public web site after less than two days of operation due to software problems. The new site allowed web site visitors instant access, for a small fee, to their personal credit reports. However, a number of initial users ended up viewing each others' reports instead of their own, resulting in irate customers and nationwide publicity. The problem was attributed to "...unexpectedly high demand from consumers and faulty software that routed the files to the wrong computers."

16· In November of 1996, newspapers reported that software bugs caused the 411 telephone information system of one of the U.S. RBOC's to fail for most of a day. Most of the 2000 operators had to search through phone books instead of using their 13,000,000-listing database. The bugs were introduced by new software modifications and the problem software had been installed on both the production and backup systems. A spokesman for the software vendor reportedly stated that 'It had nothing to do with the integrity of the software. It was human error.'

17· On June 4 1996 the first flight of the European Space Agency's new Ariane 5 rocket failed shortly after launching, resulting in an estimated uninsured loss of a half billion dollars. It was reportedly due to the lack of exception handling of a floating-point error in a conversion from a 64-bit integer to a 16-bit signed integer.

18· Software bugs caused the bank accounts of 823 customers of a major U.S. bank to be credited with $924,844,208.32 each in May of 1996, according to newspaper reports. The American Bankers Association claimed it was the largest such error in banking history. A bank spokesman said the programming errors were corrected and all funds were recovered.

19· Software bugs in a Soviet early-warning monitoring system nearly brought on nuclear war in 1983, according to news reports in early 1999. The software was supposed to filter out false missile detections caused by Soviet satellites picking up sunlight reflections off cloud-tops, but failed to do so. Disaster was averted when a Soviet commander, based on a what he said was a '...funny feeling in my gut', decided the apparent missile attack was a false alarm. The filtering software code was rewritten.

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What is V - Model - Advantages, Disadvantages And When to use it

V - Model :- V - Model testing means "Verification and Validation Model". Like the Waterfall model, the V shaped life cycle is a sequential path of execution of processes. Each phase should be completed before the next phase begins. Testing of the product is done parallel with a corresponding phase of SDLC. That is also called Review, Inspection or Static Testing.
When to use V - Model :-
Where time and cost is the constraints of the project then, we can use such models for quick and cost effective delivery. In comparison with Waterfall model, V model is more or less the same, but the activity of testing starts very early. Whcih leads to less time and cost of the project.

Let's discuss Verification and Validation Phase in detail :- 

Verification Phase :-

1. BRS (Business Requirement Specification) :- This phase includes studying the product requirements from the customer perspective.
2. SRS (System Requirement Specification) :- Deals with understanding and detailing the hardware and communication setup for the product under development.
3. HLD (High Level Design) :- SRS can be broken down further into modules taking up different functionality which is also referred to as High Level Design. It is also called Architectural Design.
4. LLD (Low Level Design) :- The internal design for all the system modules is listed out and is also known as LLD. It is also called Module Design.
5. Coding :- In this phase developer writes code.

                        Validation Phase :-

1. Unit Testing :- Unit test cases that were created in the Low Level Design phase are executed in Unit Testing. Unit Testing is conducted by developers only. In this testing, developer test code to find out any bugs or problem in the particular unit or module.

2. Integration Testing :- In Integration Testing the integration test cases which were created in the Architectural or High Level Design phase are executed. In this phase, we integrate more then one unit or module together to find out any cause or bug during  the interconnection of different different units or modules together. This phase is conducted by developer and tester both.

3. System Testing :- In System Testing functional and non-functional test cases are executed. This testing is associated with System Requirement Specification (SRS) phase. In this tester checks the entire system for its correctness and completeness.

4. Acceptance Testing :- Acceptance Testing is conducted to make sure that the Business Requirement Specification (BRS) are met in the user environment. In this testing we also uncover the compatibility and non-functional issues like performance, load, stress etc.

Advantages of V-Model :- 

* It is very good approach to choose V-Model, where projects are small and easy to understand. As it is very easy to use.

* In V-Model one phase is completed before the next phase is begin.

* Works well where Requirements are clearly defined.

* Easy to manage due to robustness of the model.

Disadvantages of V-Model :-

* High risk and less flexibility.

* Not a good model for large and complex projects.

* Not good where requirements are frequently change.

* Working software is not available until the last phase of the life cycle.

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Phases of Software Development Life Cycle (SDLC)

Let us explain each stages of Software Development Life Cycle (SDLC) :-

1. Requirement Gathering/Analysis :- In this initial phase Top level management of the development company or a Business Analyst will collect all the information from the end-user or customer. Then prepare BRS and SRS documents.
BRS (Business Requirement Specification):- BRS is nothing but a document which consists of correct and complete requirements to develop a new s/w.
SRS (Software/System Requirement Specification):- SRS is also a document that specifies the, how to develop a new s/w.

2. Design :- In design phase HLD document and LLD document is prepared.
HLD (High Level Design or Architectural Design):- This document provides overall architecture of s/w in diagrammatic notation.
LLD (Low Level Design):- This document specifies internal logic of each and every module or functionality in diagrammatic notation.

Note:[HLD is software Level, and LLD is Module LEvel Design].

3. Coding :- In this phase coding part is started. This is one of the longest phase of SDLC. Coding phase is also known as Development phase.

4. Testing :- Testing phase is basically done by Testers or Test Engineers. In this phase testers performed different kind of testing. In this, testers assure by testing an application that the build given by developer to the testing team is fulfill end-user expectations.

5. Implementation :- After testing the software developer and tester will deploy and implement the developed software or application for the customer or end-user use. This phase also known as a Deployment phase.

6. Maintenance :- After deployment of an application or product on customer end, customer starts using that application or product. So if any changes is required further, it comes under Maintenance. In short:- We as a software company care and support of that developed product or an application. This phase also known as a Support phase.

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