moduleNameMapper only works with regexes matching the whole path

[fson]

Do you want to request a feature or report a bug?

Bug

What is the current behavior?

The moduleNameMapper configuration only works with regexes that match the whole path. I found this out when working on facebook/create-react-app#584. When using this configuration the modules were stubbed correctly:

    moduleNameMapper: {
      '^.+\\.(jpg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm)$': resolve('config/jest/FileStub.js'),
      '^.+\\.css$': resolve('config/jest/CSSStub.js')
    },

But changing it to following caused them to not be stubbed:

    moduleNameMapper: {
      '\\.(jpg|png|gif|eot|otf|webp|svg|ttf|woff|woff2|mp4|webm)$': resolve('config/jest/FileStub.js'),
      '\\.css$': resolve('config/jest/CSSStub.js')
    },

Upon further investigation, I found out that this line in jest-resolve uses the same regex to replace the module name with the mapped name, and if the regex doesn't match the whole path, it doesn't get replaced correctly.

What is the expected behavior?

Expected to be able to use regexes like \\.css$ that only match the end of the path.

[cpojer]

Yes that is indeed a bug! Is this something you (or anyone else who is running into this) could help out with? The code should be somewhere around here: https://github.com/facebook/jest/blob/2699ed50ae4f849dfc384d3a4f4c4687b9fb24b0/packages/jest-resolve/src/index.js#L201

[zackargyle]

I can take a stab. 👍 Seems like it might be a really easy fix.

[zackargyle]

PR up for fix: #1723

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