let the script processer pick custom transformers when present

e2e/__projects__/custom-transformers/babel-transformer.js

@@ -0,0 +1,4 @@
+const { createTransformer } = require('babel-jest')
+module.exports = createTransformer({
+  presets: ['@babel/preset-env']
+})

lib/process-style.js

@@ -59,10 +59,8 @@ module.exports = function processStyle(stylePart, filename, config = {}) {
     getGlobalResources(vueJestConfig.resources, stylePart.lang) +
     stylePart.content
 
-  const transformer = getCustomTransformer(
-    vueJestConfig['transform'],
-    stylePart.lang
-  )
+  const transformer =
+    getCustomTransformer(vueJestConfig['transform'], stylePart.lang) || {}
 
   // pre process
   if (transformer.preprocess) {

lib/process.js

@@ -10,19 +10,21 @@ const path = require('path')
 const getVueJestConfig = require('./utils').getVueJestConfig
 const logResultErrors = require('./utils').logResultErrors
 const stripInlineSourceMap = require('./utils').stripInlineSourceMap
+const getCustomTransformer = require('./utils').getCustomTransformer
 const throwError = require('./utils').throwError
 const babelTransformer = require('babel-jest')
 const compilerUtils = require('@vue/component-compiler-utils')
 const convertSourceMap = require('convert-source-map')
 const generateCode = require('./generate-code')
 
-function resolveTransformer(lang, vueJestConfig) {
+function resolveTransformer(lang = 'js', vueJestConfig) {
+  const transformer = getCustomTransformer(vueJestConfig['transform'], lang)
   if (/^typescript$|tsx?$/.test(lang)) {
-    return typescriptTransformer
+    return transformer || typescriptTransformer
   } else if (/^coffee$|coffeescript$/.test(lang)) {
-    return coffeescriptTransformer
+    return transformer || coffeescriptTransformer
   } else {
-    return babelTransformer
+    return transformer || babelTransformer
   }
 }
 

lib/typescript-transformer.js

@@ -29,10 +29,8 @@ module.exports = {
         plugins: [require('@babel/plugin-transform-modules-commonjs')]
       }
     }
-    const customTransformer = getCustomTransformer(
-      vueJestConfig['transform'],
-      'js'
-    )
+    const customTransformer =
+      getCustomTransformer(vueJestConfig['transform'], 'js') || {}
     const transformer = customTransformer.process
       ? customTransformer
       : babelJest.createTransformer(

lib/utils.js

@@ -93,7 +93,7 @@ const getCustomTransformer = function getCustomTransformer(
     }
     return transformer
   }
-  return {}
+  return null
 }
 
 const throwError = function error(msg) {

package.json

@@ -21,7 +21,7 @@
     "format": "prettier --no-semi --single-quote --write '**/*.{js,json,md}'",
     "format:check": "prettier --no-semi --single-quote --check '**/*.{js,json,md}'",
     "lint": "eslint --ignore-path .gitignore '{,!(node_modules)/**/}*.js'",
-    "lint:fix": "npm run lint -- --fix",
+    "lint:fix": "npm run lint --fix",
     "release": "semantic-release",
     "test": "npm run lint && npm run format:check && npm run test:e2e",
     "test:e2e": "node e2e/test-runner"