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Software Testing – Defect Density

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  • Difficulty Level : Basic
  • Last Updated : 27 Mar, 2022
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Every software is assessed for quality, scalability, functionality, security, and performance, as well as other important factors. In a system testing procedure, it’s typical to find flaws and faults. Developers must, however, verify that they are addressed before releasing it to end-users. This is because correcting an inaccuracy at an initial point is far less expensive than correcting it later. The defect identification procedure guarantees that the final product meets all of the client’s requirements and standards. To guarantee that software is flawless, software developers use the defect density function to find the software’s quality.

Thus, in a nutshell, it can be concluded that Quality is inversely proportional to Defects (as the no of defects increases, the software quality decreases). In this article, we will discuss the following things:

  1. What is Defect Density?
  2. Steps to Calculate Defect Density.
  3. Uses of Defect Density.
  4. Factors Affecting Defect Density Metrics.
  5. Advantages of Defect density.
  6. At what value of defect density does the software become unacceptable?

Let’s discuss each of these topics in detail.

What is Defect Density?

Defect density is a mathematical value that indicates the number of flaws found in software or other parts over the period of a development cycle. It is then split by the software’s size. In a nutshell, it’s used to determine whether or not the software will be released. 

The fault density is important in the Software Development Life Cycle(SDLC) cannot be overstated due to the following reasons:

  1. It is used to determine the number of software flaws. 
  2. The testing team will be able to hire a third-party inspection crew for re-engineering and substitutions. 
  3. Developers can also use defect density to identify components that are prone to faults in the future. 
  4. As a consequence, testers can focus on the proper areas and provide the highest return on investment with little resources.

The defect density of software is estimated by dividing the sum of flaws by the size of the software.

Defect Density = Total Defect/Size 

Formula to calculate defect density:

Defect Density = Average number of Defects/KLOC 

Here, KLOC is Line of codes per thousands

One flaw per 1000 lines (LOC) is deemed acceptable, according to best practices. The KLOC defect density standard is one such example. Function Points are used to measure the size of software or code (FP).

Steps to Calculate Defect Density

Let’s consider an example to calculate the defect density in software.

The software has the following integrated modules with respect to the specifications. Each module has the following number of bugs discovered:

  1. Module 1 = 5 Bugs
  2. Module 2 = 10 Bugs
  3. Module 3 = 20 Bugs
  4. Module 4 = 15 Bugs
  5. Module 5 = 5 Bugs

Total bugs = 5+10+20+15+5
                  = 55

The total line of code for each module is:

  1. Module 1 = 500 LOC
  2. Module 2 = 1000 LOC
  3. Module 3 = 1500 LOC
  4. Module 4 = 1500 LOC
  5. Module 5 = 1000 LOC

Total LOC = 500+1000+1500+1500+1000
                   = 5500

The Defect Density is calculated as:

Defect Density = (55/5500) 
                          = 0.01 defects/LOC 
                          = 10 defects/KLOC

Uses of Defect Density

For the development of software and its components, defect density is regarded as an industry standard. The following are some of the uses of the defect density:

  1. It includes a development procedure for calculating the number of flaws, which allows developers to identify weak regions that need to be thoroughly tested.
  2. Organizations also desire fault density when releasing a product and comparing performance, security, quality, scalability, and other factors. Once faults have been identified, developers may begin making improvements to decrease the number of defects. 
  3. The defect density approach aids developers in determining the impact of a reduction on software quality.

In many aspects, the usage of fault density is insignificant. Developers, on the other hand, can use this model to estimate the remaining problems once they’ve built up common defects. Developers can use this approach to create a database of commonly used terms.

Factors Affecting Defect Density Metrics

The Defect density is calculated by dividing total faults by software size. The idea is to find problems that are genuinely important, not just any defects. As a consequence, it’s critical to comprehend the components that lead to a successful outcome. Before beginning this procedure, developers and the testing team must set up all of the essential circumstances. This enables developers to accurately track the impacted locations, resulting in very accurate findings.

Factors affecting density are:

  • Types of flaws
  • The code utilized is critical and sophisticated.
  • The developer’s and testing team’s abilities
  • Calculating the defect density takes time.
  • The software’s efficiency and performance are the most important factors to consider.

Advantages of Defect Density

For software testers and developers, defect density has various advantages. It meets a wide range of technical and analytical needs in addition to offering superior fault measuring accuracy. Having precise findings on hand can assist software engineers to maintain confidence in the quality and performance of their built program. Other benefits of defect density include-

  • The ability for developers to assure that the product is ready for launch does not require any more testing.
  • Developers and testers may estimate the amount of testing and rework that will be needed to correct the mistakes.
  • Testers can track down and identify components that pose a high danger.
  • The testing team can figure out how much training is needed to finish the procedure.
  • It is possible to detect and correct areas that want improvement.

At what value of defect density does the software become unacceptable?

There are no such industrial pre-defined norms about the range of defect densities, but a higher value of defect density results in the unacceptability of the proposed software. Yet, a suitable range as per the current IT industry trends would be in the range between 0.1-0.5 Defect/LOC, after this range software is not accepted as per this standard.

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