The answer lies in your question itself :)
Make sure your preprocessor is set up correctly and ensure your 'preprocessorIgnorePatterns' configuration is correct: facebook.github.io/jest/docs/api.html
You need to add some code to ignore out the import of less files:
// package.json
"jest": {
"scriptPreprocessor": "path/to/jest-preprocessor",
...
}
// jest-preprocessor.js
var babelJest = require("babel-jest");
module.exports = {
process: function(src, filename) {
return babelJest.process(src, filename)
.replace(/^(require|import).*\.less.*;$/gm, '');
}
};
Hope this helps.