🔎 Nx is a set of Extensible Dev Tools for Monorepos.

It is very common that when a project grows rapidly, it is sought to minimize the amount of errors that can be injected into production code.

The development team or the rockstar developer always seeks to have a very good result in the coverage of tests but this does not mean that this does not mean that it is 100% free of bugs or that the tests are strong to changes.

To address that, you opt for techniques such as mutation testing which seeks to generate different variations (mutations) of our tests and check how fragile the project changes.

Mutation testing is a fault-based testing technique where variations of a software program are subjected to the test dataset. This is done to determine the effectiveness of the test set in isolating the deviations.[1]

The most common are:

• Arithmetic operator replacement (+,-,/,*,%)
• Logical connector replacement (&&, ||, ===,===)
• Statement removal
• Relational operator replacement (<=, >=)
• Absolute value insertion, etc. ( value)

See Complete List

If the test survives a variation we say that the generated mutant survived.

One of the most common tools it's stryker, It support many programming languages:

• Javascript
• .NET

Notes:

• Mutation testing does not replace unit tests, rather they prove how resistent they are to changes.

• Mutation testing checks the effectiveness of the unit tests against the different variations, this means that it is based on the unit tests.

This repository contains practical examples of using the Sticker.io tool an an angular builder to mutation testing capabilites to Nx Workspaces.

Nx supports mutation testing as part of their core packages.

You need add to your workspace:

• Stryker
  • ng add @nrwl/stryker

Run ng g @nrwl/angular:app my-app to generate an application.

There are two ways to use stryker in your project, one is with the stryker.config.js or use it over angular.json.

Run ng g stryker my-app to generate the stryker config for my-app.

You can modify the angular.json - mutate target to pass it the configuration without explicit use stryker.config.js

It accepts most of the same parameters.

Run ng run my-app:mutate to start the mutants.

Run ng affected --target=mutate

Visit the Nx Documentation to learn more.