'rxjs' module not found while running Jest test suite - jestjs

Question

I have a Nest JS application for which I am writing tests for some of the Provider classes. The beforeAll fn. of jest defined in my *.spec.ts file runs fine but the jest todo() fn. fails with the following error:
Cannot find module 'rxjs' from 'node_modules/#nestjs/common/cache/interceptors/cache.interceptor.js'
Require stack:
node_modules/#nestjs/common/cache/interceptors/cache.interceptor.js
node_modules/#nestjs/common/cache/interceptors/index.js
node_modules/#nestjs/common/cache/index.js
node_modules/#nestjs/common/index.js
node_modules/#nestjs/testing/testing-module.builder.js
node_modules/#nestjs/testing/test.js
node_modules/#nestjs/testing/index.js
src/bookmark/test/integration/bkm.service.int-spec.ts
at Resolver._throwModNotFoundError (node_modules/jest-resolve/build/resolver.js:491:11)
at Object.<anonymous> (node_modules/#nestjs/common/cache/interceptors/cache.interceptor.js:5:16)
My package.json has rxjs defined in the "dependencies" section with a version of ^7.2.0.
My test in the *.spec.ts testing class looks like this:
describe('BookmarkService Integration', () => {
let prisma: PrismaService;
let bookmarkService: BookmarkService
beforeAll(async () => {
const moduleRef = await Test.createTestingModule({
imports: [AppModule],
}).compile();
prisma = moduleRef.get(PrismaService);
bookmarkService = moduleRef.get(BookmarkService);
await prisma.cleanDatabase();
});
it.todo('Default test pass')
})
I have not tried explicitly doing a npm install of rxjs since I don't understand the consequence of installing it when it already came as a default dependency when I initialized my Nest application. Any help would be greatly appreciated.
Thanks

Answer 1

Cannot find module is a common error that is thrown when a dependency requested by your project code or by one of the imported modules cannot find the target module inside the node_module directory.
This issue can be caused by a multitude of scenarios, but going by your response to my comment, it was likely caused by the fact that npm had cached the package-lock.json properties and upon rerunning npm install would still add incorrect modules to the node_modules directory. Hence the resolution is a simple deletion of the node_modules directory, the package-lock.json file and the rerunning of the npm install command.
To answer your question on how this was still a problem even when package-lock.json did contain the rxjs library reference, there could have been a number of scenarios that I would have to speculate; for one, what you were inspecting could have been a transitive rxjs dependency which is being used by another library and is not the rxjs library that is actually being requested for in the error. Alternatively, there is a chance that even though rxjs was defined in the package-lock.json file, it may not have actually been present in the node_modules directory as it may have failed to install. This really depends on the exact sequence of things that you have done prior to seeing the issue, but I hope my explanation clarifies the problem you were facing.