Reliability Testing In Software Testing: How Is It Done?


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Reliability Testing in Software Testing is a method of software testing used to assess a software's ability to operate under environmental circumstances. It allows uncovering issues in software design and functionality. It is characterized as a type of software testing that defines if the software can perform a failure-free operation for a particular period in a specific environment. It ensures that the product is free from defects and is fit for its intended function.

Factors influencing reliability testing in software testing

Below are the factors influencing reliability testing in software testing:

  1. The number of flaws detected in the software.
  2. The way users operate the system
  3. Reliability testing is a key factor towards better software quality as it helps in discovering problems in software design and functionality.
  4. The main objective of product reliability testing is to determine whether or not the software satisfies the needs of the client.
  5. Reliability testing is performed at several levels. Complex systems are tested at the unit, assembly, subsystem, and system levels.

Why do reliability testing?

According to the reliability testing definition it is used to evaluate the performance of software under specific situations. Reliability testing aims to:

  1. To find the structure of repeating failures.
  2. To determine the number of failures that occur in a given duration of time.
  3. To discover the main cause of failure.
  4. Conduct performance testing of various models of software applications after fixing their defects.

After the release of the product, the possibility of the occurrence of defects can be minimized and the software reliability can be improved. Some useful tools for this are Trend Analysis, Orthogonal Defect Classification, and Formal Methods.

Types of reliability testing

Software reliability testing methods incorporate feature testing, load testing, and regression testing.

Feature testing

Feature testing checks the features provided by the software and is conducted by following the given steps:

  1. Every operation in the software is carried out at least once.
  2. Interaction between two operations is reduced.
  3. Each operation should be checked for its proper execution.

Load testing

Generally, the software performs better at the beginning of the process, and then it starts degrading. Load testing is conducted to check the performance of software under the maximum workload.

Regression testing

Regression testing is used to check if any new bugs have been introduced because of fixing previous ones. Regression testing is conducted after every employee change or update of software features and their functionalities.

How to do reliability testing in software testing?

Reliability testing methods are expensive when you compare it to other types of testing. So, proper planning and management are required while performing reliability testing. It includes a testing process to be implemented, data for a test environment, a test schedule, and test points.

To begin with reliability testing, a tester must remember the following:

  1. Establishment of reliability goals.
  2. Development of an operational profile. 
  3. Planning and executing tests
  4. Using test cases to drive decisions.

Reliability testing can be performed using three categories-Measurement, Modeling, and Improvement.

Some key parameters involved in product reliability testing are:

  1. Probability of failure-free operation
  2. Length of time of failure-free operation.
  3. The environment in which it is executed.

Step 1: Modeling

Software modeling techniques are divided into two subcategories:

  1. Prediction modeling
  2. Estimation modeling

Meaningful results are obtained by applying suitable models.

Assumptions and abstractions can be made for simplifying problems, and no single model is suitable for all situations.

Step 2: Measurement

You can not measure software reliability directly as other related factors are considered to estimate software reliability. There are four types of software reliability measurement techniques:

1. Product metrics

Product metrics are a combination of four types of metrics:

  1. Software size: Line of Code (LOC) is an initial approach to measuring the size of the software. Only the source codes are counted in this matrix, and comments and other non-executable statements are not counted.
  2. Function point metric: It is a method for measuring the functionality of software development. It will take into account the number of inputs, outputs, master files, and so on to measure all the features provided to the user, regardless of the programming language.
  3. Complexity: The representation of complexity is critical as it is closely connected to software stability. Using a complexity-oriented metric will reduce the code to graphical representation by identifying problems in a program’s control structure.
  4. Test coverage metrics: It is a method of evaluating the authenticity of software products by performing complete tests of software products. It is the function of evaluating whether or not a system has been completely verified and tested.

2. Project Management Metrics

  1. Researchers have realized that management could result in better products.
  2. Good management could achieve higher reliability by using a better development process, risk management, and configuration management process.

3. Process Metrics

The procedure determines the quality of a product. Process metrics might be used to estimate, monitor, and improve software dependability and quality.

4. Fault and failure metrics

This metric is mostly used to determine if the system is entirely fault-free. To accomplish this goal, the types of defects discovered throughout the testing process, as well as the problems reported by users after delivery, are gathered, summarized, and evaluated.

The mean time between failures(MTBF) in software is used to assess its dependability. MTBF consists of:

  1. Mean to Failure (MTTF): The difference in time between two consecutive failures
  2. Meantime to repair (MTTR): the time required for fixing the failure.


The liability for good software is any number between 0 and 1. When errors or bugs from the program are removed reliability will increase.

Step 3: Improvement

Improvement is completely dependent on the problems that occur in the application or system, or else the characteristics of the software. The way of improvement differs according to the complexity of the software module. The major restrictions that limit the efforts made into improving software dependability are time and funding.


Reliability Testing in Software Testing is expensive when compared to other forms of testing. Hence, to perform it cost-effectively, a proper test plan and test management should be followed. In SDLC, reliability testing plays an essential role. Using the reliability metrics will be the liability of the software and predict the future of the software. If the software has high complexity then software reliability will be hard to obtain.

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