test: add lint rule to prevent new snapshot tests

[cortisiko]

Description

Adds an ESLint enforcement to phase out Jest file-based snapshots.

Test files (.test./.spec.) now error on expect(...).toMatchSnapshot() via jest/no-restricted-matchers, encouraging toMatchInlineSnapshot() or explicit assertions instead.

Changelog

CHANGELOG entry:

Related issues

Fixes:

Manual testing steps

Feature: my feature name

  Scenario: user [verb for user action]
    Given [describe expected initial app state]

    When user [verb for user action]
    Then [describe expected outcome]

Screenshots/Recordings

Before

After

Pre-merge author checklist

• I've followed MetaMask Contributor Docs and MetaMask Mobile Coding Standards.
• I've completed the PR template to the best of my ability
• I've included tests if applicable
• I've documented my code using JSDoc format if applicable
• I've applied the right labels on the PR (see labeling guidelines). Not required for external contributors.

Pre-merge reviewer checklist

• I've manually tested the PR (e.g. pull and build branch, run the app, test code being changed).
• I confirm that this PR addresses all acceptance criteria described in the ticket it closes and includes the necessary testing evidence such as recordings and or screenshots.

---

Note

Low Risk
Low risk: adds a test-only ESLint restriction and a devDependency update; no runtime code paths are affected. Potential friction is limited to new/modified Jest tests that currently use toMatchSnapshot().

Overview
Adds a new ESLint override for *.test.*/*.spec.* files that errors on expect(...).toMatchSnapshot(), pushing tests toward toMatchInlineSnapshot() or explicit assertions to phase out file-based snapshots.

Updates tooling by adding eslint-plugin-jest (and lockfile resolution) to support the new lint rule.

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[github-actions]

🔍 Smart E2E Test Selection

• Selected E2E tags: None (no tests recommended)
• Selected Performance tags: None (no tests recommended)
• Risk Level: low
• AI Confidence: 98%

click to see 🤖 AI reasoning details

E2E Test Selection:
The changes in this PR are purely developer tooling/linting configuration:

1. package.json: Added eslint-plugin-jest as a devDependency. This is a linting tool only used during development/CI linting checks, not bundled into the app.

2. .eslintrc.js: Added a new ESLint rule for test files (*.test.*, *.spec.*) that disallows toMatchSnapshot() in favor of toMatchInlineSnapshot(). This is a code quality enforcement rule that only affects the linting step, not runtime behavior.

3. yarn.lock: Updated automatically to reflect the new dependency.

None of these changes affect:

• Application runtime code or behavior
• UI components, rendering, or user flows
• Controllers, state management, or Engine
• Navigation or screen transitions
• E2E test infrastructure or test execution
• Any feature that E2E tests validate

These changes have zero impact on E2E test outcomes. No E2E tags need to run.

Performance Test Selection:
The changes are purely ESLint/linting configuration changes (adding eslint-plugin-jest and a new rule to prevent file-based snapshots). There is no impact on app performance, rendering, state management, or any runtime behavior. No performance tests are needed.

View GitHub Actions results

[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	npm/​eslint-plugin-jest@​29.14.0 ⏵ 29.15.1	+1			-2

View full report

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud