Bug demo repo for when Jest encounters an import of any file that isn't present in a barrel file.
This comes from the order of the root/parent, and the child/wildcard path being opposite of what they should be in the moduleNameMapper field. (e.g. the parent is configured first, so no import will get matched to the more specific child path).
I have reproduced this by commenting out the generated export of some-lib.service from its associated index.ts barrel file, and importing it into a .spec file. When running yarn test it will then error that the imported value is undefined (but won't have any error about unknown module paths).
The problem occurs from the following snippet (in package.json from the jest block):
"moduleNameMapper": {
"@app/some-lib": "<rootDir>/libs/some-lib/src",
"@app/some-lib/(.*)": "<rootDir>/libs/some-lib/src/$1"
}This results in the 'yarn test' command throwing TypeError: Cannot read property 'someMethod' of undefined
Reverse the order of the previous snippet, so that the more specific path comes first. This way the non-barreled imports will resolve properly under jest and won't result in 'undefined' import values:
"moduleNameMapper": {
"@app/some-lib/(.*)": "<rootDir>/libs/some-lib/src/$1",
"@app/some-lib": "<rootDir>/libs/some-lib/src"
}See official Jest docs for details:
"The order in which the mappings are defined matters. Patterns are checked one by one until one fits. The most specific rule should be listed first."