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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"node:test coverage attempts to cover mocked modules","articleBody":"### Version\n\nv22.22.0, v24.13.0, v25.6.0\n\n### Platform\n\n```text\nDarwin 25.2.0 Darwin Kernel Version 25.2.0:\n```\n\n### Subsystem\n\n_No response_\n\n### What steps will reproduce the bug?\n\nI've been seeing some odd behaviour in the test coverage report when mocking modules. This issue is very similar to #59112 however there's an edge case that was possibly missed in the fix.\n\nIf you mock a CommonJS module that's being imported into an ESM module, the coverage report includes the code from the mocked module. This is easier to demonstrate with code, [I have a reduced test case here](https://github.com/rowanmanning/node-test-coverage-issue-repro) but will talk through it.\n\nGiven these files:\n\n**`dependency.cjs`:**\n```js\nthrow new Error('This should never be called');\n\nexports.dependency = function dependency() {\n\treturn 'foo';\n}\n\n// Just here to provide some uncovered code\nexports.unused = function unused() {\n\treturn 'bar';\n}\n```\n\n**`subject.mjs`:**\n```js\nimport { dependency } from './dependency.cjs';\n\nexport function subject() {\n\treturn dependency();\n}\n```\n\nand this test file:\n\n**`test.mjs`:**\n```js\nimport assert from 'node:assert/strict';\nimport { mock, test } from 'node:test';\n\nconst dependency = mock.fn(() =\u003e 'mock-return-value');\nmock.module('./dependency.cjs', { namedExports: { dependency } });\n\nconst { subject } = await import('./subject.mjs');\n\ntest('subject calls dependency', () =\u003e {\n\tassert.equal(subject(), 'mock-return-value');\n\tassert.equal(dependency.mock.callCount(), 1);\n});\n```\n\nRunning the following test command fails because coverage does not meet the 100% target:\n\n```sh\nnode --test --experimental-test-module-mocks --experimental-test-coverage \\\n    --test-coverage-branches=100 --test-coverage-functions=100 --test-coverage-lines=100 \\\n    ./test.mjs\n```\n\n```\n✔ subject calls dependency (0.512ms)\nℹ tests 1\nℹ suites 0\nℹ pass 1\nℹ fail 0\nℹ cancelled 0\nℹ skipped 0\nℹ todo 0\nℹ duration_ms 54.595125\nℹ Error: 92.86% line coverage does not meet threshold of 100%.\nℹ Error: 80.00% branch coverage does not meet threshold of 100%.\nℹ start of coverage report\nℹ -----------------------------------------------------------------\nℹ file             | line % | branch % | funcs % | uncovered lines\nℹ -----------------------------------------------------------------\nℹ dependency.cjs   |  88.89 |    66.67 |  100.00 | 9\nℹ subject.mjs      | 100.00 |   100.00 |  100.00 |\nℹ -----------------------------------------------------------------\nℹ all files        |  92.86 |    80.00 |  100.00 |\nℹ -----------------------------------------------------------------\nℹ end of coverage report\n```\n\nThe `dependency.cjs` module is definitely not imported because the error at the top of that file is never thrown as part of the test.\n\n### How often does it reproduce? Is there a required condition?\n\nSystematically\n\n### What is the expected behavior? Why is that the expected behavior?\n\nI expect to only see a module covered when it's imported directly. I expect mocked modules to not be considered part of the covered code.\n\n### What do you see instead?\n\nUnexpected lines are reported as uncovered and the coverage report includes files that were not imported as part of the test.\n\n### Additional information\n\n_No response_","author":{"url":"https://github.com/rowanmanning","@type":"Person","name":"rowanmanning"},"datePublished":"2026-02-06T15:39:10.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":0},"url":"https://github.com/61709/node/issues/61709"}