Reliability Testing For Beginners

Reliability Testing checks whether the software can perform a failure-free operation for a specified period in a particular environment. Reliability testing in software assures that the product is fault free and is reliable for its intended purpose.

Process of Reliability Testing

Step 1) Modeling

Software Modeling Technique is divided into two subcategories:

1. Prediction Modeling

2. Estimation Modeling

  • Meaningful results can be obtained by applying suitable models.
  • Assumptions and abstractions can simplify the problems, and no single model will be ideal for all the situations.
IssuesPrediction ModelEstimation Model
Data ReferenceIt uses historical data.It uses the current data from the application development.
When used in the Development CycleIt is usually created before the development phases.It is used at the later stage of the Software Development Life Cycle.
Time FrameIt predicts the reliability in the future.It indicates the reliability either for the present time or in the future time.

Step 2) Measurement

Software reliability can’t be measured directly, and hence, other related factors are considered to estimate software reliability. Software Reliability Measurement are divided into four different categories:-

1. Product Metrics:-

Product metrics are a combination of 4 types of metrics:

  • Software size: – Line of Code is an initial intuitive approach for measuring the software’s size. The source code is counted, and other non-executable statements will not rely on it.
  • Function point Metric:- It is the method for measuring software development’s functionality. It may consider the count of outputs, inputs, master files, etc. It measures the functionality that is delivered to the user.
  • Complexity:- It is related to software reliability, so representing complexity is important. The complexity-oriented metric calculates the complexity of a program’s control structure by simplifying the code into a graphical representation.
  • Test Coverage Metrics: It is a way of estimating fault and reliability by performing the complete software products test. It means the function of determining the system has been completely verified and tested.

2. Project Management Metrics- Good governance can achieve higher reliability by using a good development process, configuration management process, risk management process, etc.

3. Process Metrics

The quality of the product is related to the process. The process metrics are used to estimate, monitor, and improve software reliability and quality.

4. Fault and Failure Metrics

Fault and Failure Metrics are used to check whether the system is completely failure-free. The types of faults found during the testing process and the failure are reported by the users after delivery are collected and analyzed to achieve this goal.

Step 3) Improvement

Improvement completely depends upon the problems that occurred in the application or system or the software’s characteristics. According to the complexity of the application module, the way of improvement will also differ. Two main constraints, time, and budget, limiting the efforts are put into the software reliability improvement.

Factors affecting software reliability

  • One of the keys to higher software quality is reliability testing. This research tends to identify certain issues with the architecture and performance of the app. 
  • The primary goal of reliability testing is to validate whether the programme satisfies the customer’s reliability criteria. 
  • At many stages, reliability testing will be conducted. At unit, assembly, subsystem and device stages, complex structures will be evaluated.

Need for Reliability Testing

  • To explore the structure of repeating errors. 
  • A given period of time is used to find the number of errors occurring. 
  • To figure out the big cause of failure 
  • Performance testing of multiple software application modules after repairing bugs.

Types of Reliability Testing

Feature Testing

Featured Testing verifies the feature provided by the software. It includes the following steps

  • Each operation in the application is executed at least once.
  • Interaction between the two processes is reduced.
  • Each method has to be verified for its proper execution.

Load Testing

The application will perform better at the start of the process, and after that, it will start degrading. It is conducted to check the performance of the software under the maximum workload.

Regression Test

It is mainly used to check whether new bugs have been introduced because of the fixing of previous bugs. Regression Testing is conducted after every change or update of the software features and their functionalities.

Methods for Reliability Testing

Testing for reliability means exercising an application to discover and remove failures before the system is deployed.

There are three approaches used for Reliability Testing.

  • Test-Retest Reliability
  • Parallel Forms Reliability
  • Decision Consistency

Test-Retest Reliability

A single group of examinees will only perform the testing process. The time should be less so that the examinee’s skills in the area can be assessed. This type of reliability demonstrates which a test can produce stable, consistent scores across time.

Parallel Forms Reliability

Many exams have multiple question papers; these parallel forms of exam provide Security. The examinee’s scores on the two test forms are correlated to determine how similar the two test forms function.

Decision Consistency

After doing this, you will see examinees either to pass or fail. It is the reliability of this classification decision that is estimated in decision consistency reliability.

Tools for Reliability Testing

CASRE (Computer-Aided Software Reliability Estimation Tool)

CASRE reliability measurement tool is based on the existing reliability models, which help in better estimations of an application product’s reliability. The GUI of the device offers a better understanding of application reliability, and it is very easy to use.


  • Print the failure result.
  • Save the work to disk.
  • Select the reliability models.
  • Select the correct model for the result.


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What are the factors influencing Reliability?

The number of faults present in the application.
The way users operate the system.

Why perform Reliability Testing?

The objective behind performing reliability testing are,
To find the structure of repeating failures.
To find the number of losses occurring in the specified amount of time.
To discover the cause of failure
To conduct testing of various modules of software application after fixing a defect

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