Reliability Testing: Methods, Tools, Example

The word 'reliable' means something that is 'dependable' and 'trustworthy.' In other words, a dependable product lives up to its expectation regardless of how much we use it. In software testing, Reliability testing is a process to know whether software can perform as expected under a given environment. 

Reliability Testing Example

Let's say you are a graphics designer. So, you may need a PC to run for at least 7-8 hours per day with its full capability without crashing. Reliability testing is the process that can determine whether the PC you are about to purchase can works flawlessly for long hours or not.

In testing, testers and developers test the reliability of an app or system as per several factors. For example, if the app can handle heavy user traffic and requests for several hours without crashing down or not.

What are the objectives of Reliability Testing?

Reliability testing can help developers to evaluate the overall performance of a software application.

The objectives of Reliability Testing are as follows −

  • To discover the numbers of failure occurred within a stipulated time

  • To figure out the primary cause of a system/application failure

  • To discover the structure of the failure

  • To execute performance testing of various modules once detects are fixed

Overall, reliability testing minimizes the possibility of system application failures after it is released in the market. It helps businesses to save money, time, and of course, brand reputation.

Types of Reliability Testing

There are three types of reliability testing conducting befitting the requirements of the client.

Feature testing − This is done explicitly for testing new applications or a new version of an existing application. In this testing, testers test all the features of the software.

It starts with testers testing each software feature in isolation, followed by testing two individual features together. They try to limit the interaction between two features ensuring no conflict arises during user experience.

Regression testing − It is preferred when a new change is introduced to an existing system. The client decides to add a new feature or modify an existing feature in the application or system. Through regression testing, one can deter if the change hampers the performance of the system.

Load testing − In load testing, an application is exposed to multiple users doing things simultaneously. This is done to ensure that the new system is ready to handle an expected load of users/traffics.

How to do Reliability Testing?

Reliability testing is conducted in three categories- modeling, measurement, and improvement. Before beginning the test, the tester must establish the reliability goals beforehand. It includes setting up the test environment, gathering data, preparing test schedules, test points, etc. 

Following are the three categories of reliability testing −

1. Modeling

The software modeling techniques are divided into two types − Prediction modeling and estimation modeling.

  • Prediction modeling −Under such models, old historical data are analyzed to predict a software failure. Testers use prediction models before starting the development phase to determine the software reliability. 

  • Estimation modeling − Such models considers data from current software development to determine the system's failure in the future. It is only conducted after executing the development process. Data are collected from the ongoing process. 

2. Measurement

It is the process where reliability metrics are measured by identifying several characteristics of the test. 

Product Metrics

Testers analyze various sources to calculate the product metrics such as the source code, design models, test cases, and requirements. The metrics are further used to dig deeper into the quality of the software. 

Some valuable metrics include −

  • Software size −Testers use the Line of Code methods such as counting the lines of source code excluding the comments and non-executable statements. 

  • Function point (FP) metric −FP metric is used to check the functionality of a developed software application. Testers use countable external inputs, external outputs, external inquiries, internal logical files, and external interface files. As an independent metric, this is a great way to determine the functional complexity of software.

  • Complexity −Testers restructure the code into a graphical form to measure the criticality of a software control structure. 

  • Test coverage −It is used to eradicate system faults by conducting a set of testing.

Project Management Metrics

This is used to analyze the quality of the management process. The key to a successful development process lies in the management style of the developer. Better management can decrease the project completion timeframe as well as reduce the development cost.

Process Metrics

It involves measuring the attributes of the software development process and improve the quality of the process.

Fault and Failure Metrics

This metrics is used to ensure the software is free from errors and system failure. In these metrics, the testing team identifies the faults. The failures here refer to the errors found by end-users. All data are accumulated and analyzed. 

The software reliability is measured via the mean time between failures (MTBF). 


  • MTTF or Mean to Failure is the time difference between two consecutive failures.

  • MTTR or Mean time to repair is the time it takes to fix a failure.

Software scores between 0 and 1 are considered as reliable, which increases when errors or bugs decrease.

3. Improvement

This is a testing process that comes after the development and before the deployment phase. In this process, testers identify the bugs and defects in the system. Tools such as Fault tree analysis and orthogonal defect classifications are used to reduce the likelihood of defects. 


Reliability testing holds paramount importance in the reliability engineering program. Undoubtedly, reliability testing is a costly process that requires proper planning and execution. It serves a much greater purpose in the software quality field, and it shouldn't be avoided at any cost.


1. What are some good Reliability Testing Tools?

Reliability testing tools are categorized as per their requirements. For reliability life data analysis, WEIBULL++ is quite promising. Similarly, RGA stands out for reliability growth analysis, while RCM is excellent for reliability-centered maintenance. Other popular reliability tools to consider- Softrel, Sorel, and SMERFS.

2. What are the Factors affecting software reliability?

Reliability testing offers numerous insights about software or system. The primary purpose of reliability testing is to discover errors in software design and functionality. 

A software can perform abnormally under several conditions −

  • Size and complexity of the code

  • Operational environment

  • Operational, training, and knowledge of the developer and the user

  • Quality of the development process

  • Specification of individual components

  • Network configuration

Updated on: 27-Apr-2021

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