Mutation Testing: Concept And Process Explained For Beginners


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Mutation testing is a type of white box testing in which testers modify specific components of an application’s source code to assure a software test suite will be able to detect changes. Changes included in the software are meant for causing errors in the program. Mutation testing is conducted for ensuring the quality of a software testing suite.

Mutation testing is usually used for conducting unit tests. The software testing aims to be able to detect all mutated codes. Mutations could then be implemented by making alterations to an existing line of code for a different value. For example, a statement can be deleted or reproduced, the true or false expression can be changed or other variables could be altered.

Concept of mutation testing

Before discussing BRCA mutation testing any further let us know about some concepts that you will be coming across:


Mutants are the mutated version of any source code. This code contains minor changes. When the mutant runs test data it should give different results from the source code. Mutants are also known as mutant programs. There are three different types of mutants:

  1. Survived mutants: Mutants that are still alive after running test data via the original and mutated variants of the source code are known as survived mutants. They are also called live mutants and should be killed.
  2. Killed mutants: Mutants killed after genetic mutation testing are known as killed mutants. These are obtained when you get different results from original and mutated versions of the source code.
  3. Equivalent mutants: Mutants that are closely linked to like mutants and they live even after passing test data through them are known as equivalent mutants they have the same meaning as the source code even if they have a different syntax.

Mutators/mutation operators

It makes mutations possible as they ride on the driver’s seat. Alteration or change to be made into the source code having a mutant version is defined by them. They are also known as faults or mutation rules.

Mutation score

Mutation score could be understood as the percentage of skilled mutants with the total number of mutants.

Mutation score = (killed mutants/total number of mutants)×100

Test cases are considered mutation sufficient if the score is 100%. Experimental results have concluded that BRAF mutation testing is an efficient approach to measure the adequacy of test cases. However, the expense of creating mutants and running each test case against the mutant program is its major disadvantage.

How to execute mutation testing?


These steps should be followed to execute mutation testing:

Step 1

Faults will be injected into the source code of the program by creating versions called mutants. Each mutant will contain a fault that makes the mutant version fail which confirms the effectiveness of test cases.

Step 2

Test cases are then applied to the original program and the mutant program. A test case should be sufficient and pinched for detecting flaws in a program.

Step 3

Analyze the results of the original and mutant programs.

Step 4

If the outputs of the original and mutant programs differ, the mutant will be killed by the test case. Therefore the test case will be good for detecting any change between original and mutant programs.

Step 5

If the output of the original and mutant programs is the same, the mutant is kept alive. In situations like these, more useful test cases for killing all mutants should be developed.

Advantages of mutation testing

Below are the advantages of mutation testing:

  1. It is a compelling approach to achieve high coverage of source programs.
  2. This testing is provided for testing the mutant program.
  3. It brings a good level of error detection for the software developer.
  4. This method reveals uncertainty in the source code and can detect all faults in the program.
  5. Customers are supported to make the most reliable and stable system.

Disadvantages of mutation testing

Below are the disadvantages of BRAF mutation testing:

  1. Due to the large number of mutant programs that must be produced, genetic mutation testing is both expensive and time-consuming.
  2. Each mutant will have an equivalent number of test cases to the original program. So a huge number of mutant programs may be tested against the original test suite.
  3. This method requires source code changes and it isn't applicable for black-box testing.

Mutation testing vs. Regression testing

Regression testing can sometimes be confused with mutation testing. Regression testing is the method of testing new changes into a program for ensuring the older program is still working with new changes. Coders of the test department will be developing code test scenarios that will test new pieces of code after being written.

Regression testing is used for testing changes in a program to ensure a new version of the application that can solve an old bug doesn't introduce another. The regression test will be looking at applications for ensuring small changes in an application’s code don't break the software. This is in contrast to code mutation, which involves making new modifications to an application's code in order to test the test suite.


Types of mutation testing

Statement mutation, decision mutation, and value mutation are the three forms of BRCA mutation testing available.

  1. Statement mutation: A developer will cut and paste a portion of the code, which may result in the loss of some lines.
  2. Value mutation: Values of primary parameters are altered.
  3. Decision mutation: Control statements will be modified.


If you want exhaustive testing of the application then the answer is mutation testing. It is one of the most comprehensive techniques for testing a program. This approach evaluates a testing program's efficacy and accuracy in discovering system flaws or mistakes.

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