Merge pull request #6 from routablehq/bugfix/jest-28-error-invalid-return-type-with-process

[Bugfix] Fix Jest version 28.x.x throwing an Error for invalid return type in process handler

Author: sebestajozef

src/helpers.js

@@ -5,6 +5,8 @@
 
 const fs = require('fs');
 const crypto = require('crypto');
+// eslint-disable-next-line import/no-extraneous-dependencies
+const jest = require('jest');
 
 const exportStartRegex = /\n:export.{\n*/;
 const exportEndRegex = /\n*}/;
@@ -43,3 +45,20 @@ module.exports.getCacheKey = () => (
     .update(fs.readFileSync(__filename))
     .digest('hex')
 );
+
+module.exports.makeProcessExports = (exportString) => {
+  // jest.getVersion() returns semantic version, like X.Y.Z
+  // We are only interested in the major version (the "X") in this case.
+  const [major] = jest.getVersion().split('.');
+  const majorInt = parseInt(major, 10);
+
+  if (majorInt < 27) {
+    // For jest versions 26.x.x and bellow, we are fine with just returning
+    // the exports as a string
+    return exportString;
+  }
+
+  // For jest version 27.x.x and above, we want to return an object with a
+  // "code" property, which contains an export string (see here: https://jestjs.io/docs/code-transformation)
+  return { code: exportString };
+};

src/index.js

@@ -25,6 +25,7 @@ const {
   hasExports,
   isSupportedFile,
   makeExportsString,
+  makeProcessExports,
   parseExportsToObject,
 } = require('./helpers');
 
@@ -50,7 +51,10 @@ module.exports = {
     }
 
     // generate the module.exports string
-    return makeExportsString(result);
+    const exportString = makeExportsString(result);
+
+    // return the process export
+    return makeProcessExports(exportString);
   },
   getCacheKey() {
     return getCacheKey();

src/index.test.js

@@ -1,5 +1,6 @@
 const fs = require('fs');
 const path = require('path');
+const jest = require('jest');
 const sinon = require('sinon');
 
 const transformer = require('./index');
@@ -21,6 +22,10 @@ const emptyModuleString = 'module.exports = {};';
 
 describe('jest-scss-transform', () => {
   describe('transformer.process', () => {
+    beforeEach(() => {
+      sinon.restore();
+    });
+
     it('returns empty module for file extensions other than .scss', () => {
       expect(transformer.process(contentsIncorrectExt, incorrectExtFile)).toBe(emptyModuleString);
     });
@@ -40,6 +45,14 @@ describe('jest-scss-transform', () => {
     it('processes files with poorly formatted exports', () => {
       expect(transformer.process(contentsFormatting, formattingFile)).toBe(expectedParsed);
     });
+
+    it.each(['27.0.0', '27.5.2', '28.0.0', '28.0.1'])(
+      'returns object with code property for jest versions %s and above',
+      (jestVersion) => {
+        sinon.stub(jest, 'getVersion').returns(jestVersion);
+        expect(transformer.process(contentsBasic, commentsFile)).toEqual({ code: expectedParsed });
+      },
+    );
   });
 
   describe('transformer.getCacheKey', () => {