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swc/jest - maximum (out of) coverage value channges based on tests run #112
Description
When running Jest tests with coverage enabled, reporters such as text text-summary and html show a value of coverage out of a maximum number. This value shouldn't change as it represents the maximum potential coverage for the files scanned by Jest from collectCoverageFrom. However it does change when I add or remove tests or if I only run a sub set of tests.
All tests:
=============================== Coverage summary ===============================
Statements : 92.38% ( 61559/66639 )
Branches : 83.83% ( 16807/20049 )
Functions : 80.31% ( 9038/11254 )
Lines : 93.07% ( 54584/58649 )
================================================================================
Single test file:
=============================== Coverage summary ===============================
Statements : 14.19% ( 7343/51748 )
Branches : 1.43% ( 287/20049 )
Functions : 2.04% ( 229/11209 )
Lines : 14.48% ( 6336/43772 )
================================================================================
I did some digging around and found what I think the problem is. The process method conditionally sets the module.type property to es6 or commonjs depending on the value of jestOptions.supportsStaticESM:
module: {
...swcOptionsForProcess.module,
type: jestOptions.supportsStaticESM
? "es6"
: ("commonjs" as any),
},
The processAsync method is almost exactly the same as the process except it doesn't do the jestOptions.supportsStaticESM check and instead just defaults to es6:
module: {
...swcOptionsForProcess.module,
// async transform is always ESM
type: "es6" as any,
},
I was able to confirm the numbers are reliably consistent when:
- Converting the project test runner to support es6 modules, or
- Hacking the
@swc/jesttransformer so that the type iscommonjsinprocessAsync
I don't know if this difference in code was an oversight or has been done on purpose but using the same logic from process in processAsync seems to give a more accurate result.
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