Could not locate module in test using @app
Published: 2024-06-26 16:58:39

I'm trying to work with tests in NestJS now and I couldn't move forward due to a problem with the location of the modules.
The application was already responding, the problems started when I tried to run the tests.

The first try gave me several errors like this:

```
Cannot find module 'src/common/dto/paginated-response.dto' from 'applications/applications.service.ts'
```

According my reading of [Tejas](https://stackoverflow.com/questions/53963007/error-while-running-nestjs-in-production-mode-cannot-find-module), I understood that the problem was the relative path starting in 'src/...'. 

Then, I read the tutorial by [Amir Mustafa](https://amirmustafaofficial.medium.com/nest-js-converting-relative-path-to-absolute-path-fea5b22dce47) for converting the relative paths to absolute paths from the configuration.

After replacing the relative paths with the `@app` key, I got to run the application, but the tests failed again. This time, the errors were like this:

```
Cannot find module '@app/users/users.controller' from 'users/users.controller.spec.ts'
```

After reading the question/answer by [dragons0458](https://stackoverflow.com/questions/61356672/error-when-i-try-to-test-with-nestjs-jest-and-graphqlfederationmodule), I understood that I should to configure moduleNameMapper inside jest section of package.json. The section is so now:

```
  "jest": {
    "moduleFileExtensions": [
      "js",
      "json",
      "ts"
    ],
    "rootDir": "src",
    "testRegex": ".*\\.spec\\.ts$",
    "transform": {
      "^.+\\.(t|j)s$": "ts-jest"
    },
    "collectCoverageFrom": [
      "**/*.(t|j)s"
    ],
    "coverageDirectory": "../coverage",
    "testEnvironment": "node",
    "moduleNameMapper": {
      "^@app/(.*)": "<rootDir>./dist/$1"
    }
  }
```

The third try gave me new errors, below, but now I don't know what I should do. It looks to me that $1 in moduleNameMapper is not converted to path. 

```
Configuration error:
    
    Could not locate module @app/gateways/gateways.controller mapped as:
    [MY HOME]/backend_nestjs/src/dist/$1.
    
    Please check your configuration for these entries:
    {
      "moduleNameMapper": {
        "/^@app\/(.*)/": "[MY HOME]/backend_nestjs/src/dist/$1"
      },
      "resolver": undefined
    }

      1 | import { Test, TestingModule } from '@nestjs/testing';
    > 2 | import { GatewaysController } from '@app/gateways/gateways.controller';
        | ^
      3 | import { GatewaysService } from '@app/gateways/gateways.service';
      4 |
      5 | describe('GatewaysController', () => {

      at createNoMappedModuleFoundError (../node_modules/jest-resolve/build/resolver.js:759:17)
      at Object.<anonymous> (gateways/gateways.controller.spec.ts:2:1)
```

The application is answering in 3000 port, but the tests (12 tests) fail. What is lacking for the correct configuration for modules?

I am pasting here two files that I think can help to understand my configuration:

**tsconfig.json**

```
{
  "compilerOptions": {
    "module": "commonjs",
    "declaration": true,
    "removeComments": true,
    "emitDecoratorMetadata": true,
    "experimentalDecorators": true,
    "allowSyntheticDefaultImports": true,
    "target": "ES2021",
    "sourceMap": true,
    "outDir": "./dist",
    "baseUrl": "./",
    "incremental": true,
    "skipLibCheck": true,
    "strictNullChecks": false,
    "noImplicitAny": true,
    "strictBindCallApply": false,
    "forceConsistentCasingInFileNames": false,
    "noFallthroughCasesInSwitch": false,
    "paths": {
      "@app/*": ["./src/*"]
    }
  }
}
```

**jest-e2e.json**

```
{
  "moduleFileExtensions": ["js", "json", "ts"],
  "rootDir": ".",
  "testEnvironment": "node",
  "testRegex": ".e2e-spec.ts$",
  "transform": {
    "^.+\\.(t|j)s$": "ts-jest"
  }
}
```
Thank you very much.