What does mutation testing mean in software engineering?

Mutation testing is a technique that deliberately introduces small bugs into code to verify whether your test suite can detect them. It measures test effectiveness by injecting mutations like changing operators or return values, then checking if tests fail. If tests catch the mutations, your test suite is strong; if mutations survive, you have gaps in your testing.

How do you use mutation testing in a sentence at work?

You can say: 'Let us run mutation testing on the authentication module' or 'Our mutation testing score is 75 percent, which means we need stronger tests.' Use it as a noun phrase when discussing testing practices or results.

Is mutation testing formal or informal?

Mutation testing is formal technical language appropriate for code reviews, technical documentation, and professional discussions. It is not casual or slang, though it is commonly used in everyday tech conversations among developers and QA engineers.

How is mutation testing different from code coverage?

Code coverage measures the percentage of code lines executed by tests, while mutation testing measures whether tests actually verify correct behavior. You can have 100 percent code coverage but still have weak tests that do not catch bugs. Mutation testing is a more thorough quality metric.

What tools are used for mutation testing?

Popular mutation testing tools include PIT for Java, Stryker for JavaScript/TypeScript, Mutmut for Python, and Infection for PHP. Each tool injects mutations specific to the programming language and framework.

mutation testing meaning in tech

Commonness	3/5
Versatility	4/5
Formality	CasualFormalFormal
Spoken ↔ Written	SpokenWrittenBoth
Directness ↔ Diplomatic	DirectDiplomaticDirect
Region	US and UK

Say it like this

✓Let us run mutation testing to validate our test coverage

✓The mutation testing results show gaps in our test suite

✓We should improve our mutation score before shipping to production

Real examples

in a standup

"I ran mutation testing on the payment module yesterday and found that our tests were not catching edge cases with decimal values."

in a code review

"This test looks good, but let us add mutation testing to ensure we are actually validating the business logic and not just happy paths."

in a team meeting

"Our mutation testing score improved from 65 percent to 82 percent after we added those extra assertions to the authentication tests."

Don't say this

Handle with care. Often confused with regular unit testing. Mutation testing is a technique that deliberately breaks code to verify tests catch the bugs, not a way to test code for mutations or changes.

✕We used mutation testing to fix the bugs in our code.

✓We used mutation testing to identify gaps in our test suite.— Mutation testing does not fix bugs; it reveals whether tests are strong enough to catch bugs if they existed.

✕Mutation testing is the same as code coverage.

✓Mutation testing measures test effectiveness; code coverage measures which lines are executed.— Code coverage only tells you if code runs; mutation testing tells you if tests verify correctness.

✕We need mutation testing on all our legacy code right now.

✓We should apply mutation testing to critical modules first, then expand gradually.— Mutation testing is resource-intensive; prioritizing critical code is more practical.

Other forms

noun

mutation testing

"Mutation testing revealed that our validation tests were too weak."

noun

mutation score

"Our mutation score of 85 percent indicates strong test quality."

verb

run mutation testing

"Let us run mutation testing on this new feature before we merge it."

Often used with

mutation testing scorePercentage indicating how many mutations were caught by tests

run mutation testingExecute a mutation testing analysis on your codebase

mutation testing toolSoftware like PIT, Stryker, or Mutmut that performs mutation testing

mutation testing resultsOutput showing which mutations were caught and which escaped

improve mutation scoreStrengthen tests to catch more injected mutations

Similar words

test effectiveness analysisBroader term; mutation testing is a specific technique within this category

fault injectionSimilar concept but can refer to injecting faults in infrastructure or systems, not just code

Opposites

unit testingcode coverage

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Practice

Try it

4 quick exercises

Complete the sentence

1. We need to _______ our test suite to ensure it catches real bugs before production.

Spot the mistake

2. Which sentence uses mutation testing correctly?

Our mutation testing tool fixed all the bugs in the code.We used mutation testing to measure how well our tests would catch introduced defects.Mutation testing is the same thing as checking code coverage percentages.The developers mutation tested the application instead of writing proper tests.

Pick the most natural phrasing

3. How would a QA lead naturally express concern about test quality?

We should mutation testing this before launch.Let us run mutation testing on the critical modules.Mutation testing must be done immediately.I will mutation testing the code now.

Rewrite naturally

4. Rewrite this in natural tech English using mutation testing: 'We need to check if our tests are good enough by seeing if they catch small code changes.'

Questions

Quick poll

Have you said "mutation testing" in a standup this week?

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