This repository demonstrates a difference in Vitest's code coverage gathering when working with mono-repos.
If you're working with a mono-repo where internal package b depends on another internal package a, and Vitest is executed from the mono-repo root using the -r flag to define the root of the package to test, the code coverage report will include the files from a in the despite it being a dependency.
Regardless of what the current working directory is, because the -r flag is being used to point to a Vitest project root, I would expect that the --coverage flag works the same exact way.
Start off by cloning this repository and installing the dependencies using npm install
When running the tests for packages/b from that package's root, the code coverage report only includes source files from that package. You can demonstrate this by running npm test within packages/b, which prints a coverage report like this:
-------------------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
-------------------|---------|----------|---------|---------|-------------------
All files | 100 | 100 | 100 | 100 |
add-and-double.js | 100 | 100 | 100 | 100 |
-------------------|---------|----------|---------|---------|-------------------
When running the tests for packages/b from the workspace root -- which is supported by the -r flag -- the coverage report includes the files for packages/a as well as the expected ones from packages/b. You can demonstrate this by running npm test from the workspace root, which prints a coverage report like this:
--------------------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
--------------------|---------|----------|---------|---------|-------------------
All files | 100 | 100 | 100 | 100 |
a/src | 100 | 100 | 100 | 100 |
add.js | 100 | 100 | 100 | 100 |
index.js | 100 | 100 | 100 | 100 |
b/src | 100 | 100 | 100 | 100 |
add-and-double.js | 100 | 100 | 100 | 100 |
--------------------|---------|----------|---------|---------|-------------------
There is a coverage.excludes configuration option that can be used to exclude certain source files from the coverage report. However, it is unclear how this would be used to exclude files from a sibling package. All of the following patterns within that option did not exclude it from the coverage report:
../anode_modules/aa
The following option did work, but is confusing from the perspective of running the tests from the packages/b directory, since it's a path relative to the workspace root.
packages/a
However, it has the side-effect of now including the test files for package/b in the coverage report. This can be resolved by spreading the configDefaults.coverage.excludes value that vitest/config exports into the excludes array, but this feels like a lot of ceremony just to restore the original behavior (and still feels weird since the packages/a path is relative to the worksace root, and one would assume that paths in the vitest.config.js file are relative to the directory it is located within, or at least relative to the directory specified by the -r flag).