[Bug]: Test coverage report broken for @storybook/nextjs

[rotous]

Describe the bug

• Create a standard NextJS project with the following command: npx create-next-app@latest
• Add Storybook with the following command: npx sb init --builder webpack5
• Add @storybook/nextjs with the following command: npm install --save-dev @storybook/nextjs@next
• Update the config in .storybook/main.js with the following line: framework: '@storybook/nextjs', (as documented on https://storybook.js.org/docs/8.0/get-started/nextjs)
• Add the test-runner with: npm install @storybook/test-runner --save-dev
• Add "test-storybook": "test-storybook" to the scripts in package.json
• Add the coverage addon with npm install @storybook/addon-coverage --save-dev
• Start Storybook with npm run storybook
• Create the coverage report with npm run test-storybook -- --coverage
• Output the report to the console with npx nyc report -t coverage/storybook/

Result:

PASS browser: chromium src/stories/Header.stories.js
PASS browser: chromium src/stories/Button.stories.js
PASS browser: chromium src/stories/Page.stories.js

Test Suites: 3 passed, 3 total
Tests: 8 passed, 8 total
Snapshots: 0 total
Time: 1.711 s, estimated 2 s
Ran all test suites.
Coverage file (2 bytes) written to .nyc_output/coverage.json

File	% Stmts	% Branch	% Funcs	% Lines	Uncovered Line #s
All files	0	0	0	0

To Reproduce

No response

System

Storybook Environment Info:

  System:
    OS: Linux 5.15 Ubuntu 22.04.3 LTS 22.04.3 LTS (Jammy Jellyfish)
    CPU: (20) x64 13th Gen Intel(R) Core(TM) i7-13700H
    Shell: 5.1.16 - /bin/bash
  Binaries:
    Node: 20.11.0 - ~/.nvm/versions/node/v20.11.0/bin/node
    npm: 10.5.0 - ~/.nvm/versions/node/v20.11.0/bin/npm <----- active
  npmPackages:
    @storybook/addon-coverage: ^1.0.1 => 1.0.1
    @storybook/addon-essentials: ^7.6.17 => 7.6.17
    @storybook/addon-interactions: ^7.6.17 => 7.6.17
    @storybook/addon-links: ^7.6.17 => 7.6.17
    @storybook/addon-onboarding: ^1.0.11 => 1.0.11
    @storybook/blocks: ^7.6.17 => 7.6.17
    @storybook/nextjs: ^7.6.17 => 7.6.17
    @storybook/react: ^7.6.17 => 7.6.17
    @storybook/test: ^7.6.17 => 7.6.17
    @storybook/test-runner: ^0.16.0 => 0.16.0
    eslint-plugin-storybook: ^0.8.0 => 0.8.0
    storybook: ^7.6.17 => 7.6.17

Additional context

The issue seems to be introduced with @storybook/nextjs@7.6.0-alpha.5. The coverage reporting works fine up until @storybook/nextjs@7.6.0-alpha.4:

Storybook Environment Info:

  System:
    OS: Linux 5.15 Ubuntu 22.04.3 LTS 22.04.3 LTS (Jammy Jellyfish)
    CPU: (20) x64 13th Gen Intel(R) Core(TM) i7-13700H
    Shell: 5.1.16 - /bin/bash
  Binaries:
    Node: 20.11.0 - ~/.nvm/versions/node/v20.11.0/bin/node
    npm: 10.5.0 - ~/.nvm/versions/node/v20.11.0/bin/npm <----- active
  npmPackages:
    @storybook/addon-coverage: ^1.0.1 => 1.0.1
    @storybook/addon-essentials: ^7.6.17 => 7.6.17
    @storybook/addon-interactions: ^7.6.17 => 7.6.17
    @storybook/addon-links: ^7.6.17 => 7.6.17
    @storybook/addon-onboarding: ^1.0.11 => 1.0.11
    @storybook/blocks: ^7.6.17 => 7.6.17
    @storybook/nextjs: ^7.6.0-alpha.4 => 7.6.0-alpha.4
    @storybook/react: ^7.6.17 => 7.6.17
    @storybook/test: ^7.6.17 => 7.6.17
    @storybook/test-runner: ^0.16.0 => 0.16.0
    eslint-plugin-storybook: ^0.8.0 => 0.8.0
    storybook: ^7.6.17 => 7.6.17

Output of $ npx nyc report -t coverage/storybook/:

File	% Stmts	% Branch	% Funcs	% Lines	Uncovered Line #s
All files	93.93	77.77	66.66	87.5
Button.jsx	100	71.42	100	100	19
Header.jsx	100	100	100	100
Page.jsx	81.81	100	50	66.66	14-15

[yamish123]

I have same issue too.

[valentinpalkovic]

Hi @rotous and @yamish123

This got very likely fixed in Storybook 8.0.6. Could you please try it out?

[yamish123]

@valentinpalkovic
Thanks! This issue is solved for me at Storybook 8.0.6.

[rotous]

Finally had time to update. The issue is fixed for me too with Storybook v8.0.8. Thanks!