[Bug]: unmatched capture groups in moduleNameMapper regexes are replaced with the string "undefined" instead of an empty string

[niklasholm]

Version

29.6.4

Steps to reproduce

1. Put this in your jest configuration

const config = {
  moduleNameMapper: {
    "^@Foobar(/.*)?$": "<rootDir>/src/components/Foobar$1", // Path to any folder with an index.js
  }
}

2. Put this in any file tested by jest

import Foobar from "@Foobar";

3. Run a test for that file.

Expected behavior

The test should execute normally.

Actual behavior

The test will fail because jest-resolve didn't find the component

  ● Test suite failed to run

    Configuration error:

    Could not locate module @Foobar mapped as:
    C:\Users\nikho\jest-test\src\components\Foobar$1.

    Please check your configuration for these entries:
    {
      "moduleNameMapper": {
        "/^@Foobar(\/.*)?$/": "C:\Users\nikho\jest-test\src\components\Foobar$1"
      },
      "resolver": undefined
    }

This is because when the capture group (/.*)? is not matched it will get the value undefined in the object returned by String.prototype.match, and this is coerced to a string instead of replaced with an empty string, so jest-resolve will try to find the component Foobarundefined instead of Foobar. Simply adding || "" to line 442 should fix the issue.

jest/packages/jest-resolve/src/resolver.ts

Lines 440 to 443 in 3738e3f

	moduleName.replace(
	/\$([0-9]+)/g,
	(_, index) => matches[parseInt(index, 10)],
	)

Additional context

No response

Environment

System:
    OS: Windows 10 10.0.19045
    CPU: (8) x64 Intel(R) Core(TM) i7-8550U CPU @ 1.80GHz
  Binaries:
    Node: 18.17.1 - C:\Program Files\nodejs\node.EXE
    Yarn: 1.22.19 - ~\AppData\Roaming\npm\yarn.CMD
    npm: 10.0.0 - ~\AppData\Roaming\npm\npm.CMD
  npmPackages:
    jest: ^29.6.4 => 29.6.4

[github-actions]

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