next/jest: Allow moduleNameMapper to match before Next.js internal ma…

…ppings (#36312)

Fixes #35634

This change doesn't require tests as importing svgs is not a supported feature, this just makes it slightly more ergonomic to override the matchers. 



## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have helpful link attached, see `contributing.md`

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have helpful link attached, see `contributing.md`

## Documentation / Examples

- [ ] Make sure the linting passes by running `yarn lint`

packages/next/build/jest/jest.ts

@@ -72,6 +72,10 @@ export default function nextJest(options: { dir?: string } = {}) {
         ...resolvedJestConfig,
 
         moduleNameMapper: {
+          // Custom config will be able to override the default mappings
+          // moduleNameMapper is matched top to bottom hence why this has to be before Next.js internal rules
+          ...(resolvedJestConfig.moduleNameMapper || {}),
+
           // Handle CSS imports (with CSS modules)
           // https://jestjs.io/docs/webpack#mocking-css-modules
           '^.+\\.module\\.(css|sass|scss)$':
@@ -84,9 +88,6 @@ export default function nextJest(options: { dir?: string } = {}) {
           '^.+\\.(png|jpg|jpeg|gif|webp|avif|ico|bmp|svg)$': require.resolve(
             `./__mocks__/fileMock.js`
           ),
-
-          // Custom config will be able to override the default mappings
-          ...(resolvedJestConfig.moduleNameMapper || {}),
         },
         testPathIgnorePatterns: [
           // Don't look for tests in node_modules