jestjs/jest

[Feature]: Detect unused stubs in test code

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#12,296 opened on Feb 3, 2022

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:rocket: Feature RequestHelp WantedPinned

Description

🚀 Feature Proposal

As described in this article, JUnit and Mockito support detecting unnecessary stubs and tell the user to remove them. It would be great to have that feature in Jest.

Motivation

Removing unused stubs makes the test code cleaner and more maintainable.

Example

No response

Pitch

Removing unused stubs makes the test code cleaner and more maintainable. This leads to users writing cleaner and more delightful tests and prevents certain errors from happening when users expect their stubs to be responsible for a specific behavior when actually they have never been called.

Contributor guide

Tech stack
jesttypescriptjavascript
Domain
testingdeveloper experience
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
3-5 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Understanding of Jest test structureBasics of mocking
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35
Research direction
Investigate how Jest currently handles stubs (mock functions) and where they are tracked. Look at the Jest source code, particularly packages/jest core and packages/jest runtime. Consider how an unnecessary stub detection mechanism could be added, similar to Mockito's UnnecessaryStubbingException. The issue references a Baeldung article for inspiration, so reviewing that may provide implementation ideas.