Reliability Testing Tutorial (What is, Methods, Tools, Example)

The chance of failure-free software execution for a set period of time in a given environment is defined as reliability.

People nowadays naively believe in any program in this mechanized environment. People believe that whatever outcome the software system produces is always correct, therefore they follow it. That is a common mistake that we all make.

Users believe that the data displayed is correct and that the software will always work properly. This is where the requirement for reliability testing arises.

Reliability Testing

Reliability testing is a software testing procedure that determines if a piece of software can operate without fail for a set period of time in a given environment. Reliability testing ensures that the software product is bug-free and capable of performing its intended function.

Reliability literally means "yielding the same." In other words, the word "reliable" suggests that something is trustworthy and will provide the same result every time. Reliability testing is the same way.

When does Reliability Testing come into play?

The following are the goals of reliability testing −

  • To figure out the pattern of recurring failures.

  • To determine the number of failures that occur over a given period of time.

  • To determine the primary reason for failure

  • After a bug has been fixed, perform performance testing on several components of the software program.

Test cases should be written in such a way that they cover all aspects of the software. The test cases should be run at regular intervals so that we can compare the current result to the previous result and see if there are any differences. If it produces the same or similar results, the software is deemed to be trustworthy.

We can also test the Reliability by running the test cases for a set amount of time and seeing if the results are displayed appropriately without any errors after that period of time. We must verify the environment restrictions such as memory leakage, low battery, low network, database issues, and so on while performing Reliability Testing.

Example of Reliability Testing

The likelihood of a retail PC remaining operational for eight hours without crashing is 99 percent; this is referred to as reliability. Reliability testing is divided into three categories.

  • Modeling

  • Measurement

  • Improvement

The likelihood of failure can be calculated using the formula below.

Probability = number of failing instances / total number of cases under evaluation

Software Reliability Influencing Factors

  • The total number of flaws in the software.

  • The way in which people deal with the system

  • One of the keys to better software quality is reliability testing. This testing aids in the detection of numerous flaws in the software's design and functionality.

  • The basic goal of reliability testing is to see if the software meets the customer's reliability requirements.

  • There will be numerous stages of reliability testing. At the unit, assembly, subsystem, and system levels, complex systems will be tested.

Types of Reliability Testing

  • Feature Testing This testing assesses appropriateness, or whether or not an application function as expected for its intended usage. It will examine an application's interoperability here in order to test it with other components and systems that interact with it. It ensures the system's accuracy by checking for flaws discovered during Beta testing. Aside from that, it checks for security and compliance. Security testing is concerned with preventing unintended or intentional unwanted access to an application. We will verify for compliance by seeing if the application meets particular criteria such as standards, rules, and so on.

  • Stress Testing Load testing will determine how well the system operates in comparison to other systems or performance. It is also determined by the number of concurrent users who utilize the system and the system's behavior toward the users. The system must respond to user commands in a timely manner (say, 5 seconds) and match user expectations.

  • Regression Testing Regression testing will determine whether the system is functioning properly and whether any flaws have been introduced as a result of the installation of new software capabilities. When a bug has been addressed and the tester needs to retest it, this is also done.

How to Test for Reliability

When compared to other types of testing, reliability testing is more expensive. As a result, when performing reliability testing, proper planning and management are essential. This contains the testing process that will be used, data for the test environment, a test schedule, and test points, among other things.

To begin reliability testing, the tester must keep track of the following items −

  • Set goals for dependability.

  • Create a profile for your operation

  • Plan and carry out testing

  • Make judgments based on test results.

Modeling, Measurement, and Improvement are the three categories in which we can execute Reliability Testing, as we described earlier.

The following are the essential parameters in Reliability Testing −

  • Failure-free operation's chances

  • Duration of non-failure operation

  • The environment in which it is carried out

Modeling Software (Step 1) Modeling Techniques are separated into two categories −

  • Prediction Modeling

  • Estimation Modeling

Appropriate models can be used to produce meaningful results.

To simplify difficulties, assumptions and abstractions can be used, but no one model can fit all scenarios.

The following are the main changes between the two models −

IssuesPrediction ModelsEstimation Models
Data ReferenceIt is based on historical data.It makes advantage of up-to-date data from the software development process.
When used in Development CycleIt is often developed before to the development and testing phases.It is most commonly utilized at the end of the Software Development Life Cycle.
Time FrameIt will be able to forecast future reliability.It will forecast reliability in the present or in the future.

Measurement (Step 2)

Because software reliability cannot be tested directly, various factors are taken into account to evaluate software reliability. There are four types of software reliability measurement methodologies now in use −

  • Product Metrics Product metrics are made up of four different categories of data −

    • Software size − The Line of Code (LOC) method is a simple way to estimate the size of the software. This measure only counts the source code; comments and other non-executable statements are not included.

    • Function Point Metric − Function Point Metrics are a way of assessing the software development's functionality. It will take into account the number of inputs, outputs, master files, and so on. It is independent of the programming language and measures the functionality provided to the user.

    • Complexity − It is directly related to software reliability; hence it is critical to describe complexity. A complexity-oriented metric determines the difficulty of a program's control structure by converting the code into a graphical representation.

    • Test Coverage Metrics − It is a way of finding fault and reliability in software products by fully evaluating them. Software reliability is the capacity to determine whether or not a system has been adequately validated and tested.

  • Project Management Metrics  Researchers have discovered that good management can lead to higherquality products. By adopting better development processes, risk management processes, configuration management processes, and so on, good management can achieve improved reliability.

  • Process Metrics The method has a direct impact on the product's quality. Software dependability and quality may be estimated, monitored, and improved using process metrics.

  • Fault and Failure Metrics Failure and Fault Metrics are mostly used to determine if a system is totally fault-free. To achieve this purpose, both sorts of errors discovered during the testing process (i.e. before delivery) and failures reported by users after delivery are gathered, summarized, and analyzed.

The mean time between failures is used to assess software dependability (MTBF). The MTBF is made up of

  • The mean time to failure (MTTF) is the time between two successive failures.

  • The mean time to repair (MTTR) is the amount of time it takes to solve a problem.

MTBF = MTTF + MTTR is a formula for calculating the maximum time between failures.

For good software, reliability is a number between 0 and 1.

When faults or defects in the program are fixed, reliability improves.

Step 3 − Enhancement

Improvement is entirely dependent on the issues that have arisen in the application or system, or on the software's features. The method of improvement will differ depending on the complexity of the software module. Two major constraints, time and funding, will limit the amount of work invested into improving software reliability.

Methods for Reliability Testing Examples

Testing for dependability is putting an application through its paces in order to identify and eliminate flaws before the system is released.

There are three main ways to Reliability Testing −

  • Test-Retest Reliability

  • Parallel Forms Reliability

  • Decision Consistency


Reliability testing is an essential component of a reliability engineering program. It is, more accurately, the heart of the reliability engineering effort.

Furthermore, during software testing, reliability tests are mostly used to reveal specific failure modes and other issues.

Reliability Testing is divided into three categories in software engineering.

  • Modeling

  • Measurement

  • Improvement

The Influence of Improvement Factors on Software Reliability

  • The total number of flaws in the software.

  • The way in which people interact with the system.

Updated on: 22-Sep-2021


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