Cypress + DOCX: Debugging the “Not Implemented” Error from Mammoth

Problem

I was trying to test the content of a downloaded .docx file in Cypress using mammoth but Cypress kept returning 'Not implemented' error which was quite confusing because the task was implemented. But after triple-checking my plugin code and re-running the test, I realized the real issue was mammoth didn’t like the .docx file I was trying to read.

After digging deeper, I learned this is a known limitation. Mammoth can choke when the DOCX file includes:

• Word fields (<w:fldSimple>)

• Smart tags

• Structured document tags (<w:sdt>)

• Comments or track changes

These elements are valid in Word, but not supported by Mammoth’s parser, hence the misleading "Not implemented" error.

Solution

Instead of relying on Mammoth, creating a simple Cypress task to extract the raw document.xml from the .docx file solved the problem. That way, I could assert the content of the file.

If you're running into that frustrating "Not implemented" error while trying to test Word files in Cypress, it's probably not your code that's broken. Most likely, the .docx itself contains something Mammoth doesn't know how to handle. Happy coding!

const unzipper = require('unzipper');

module.exports = (on, config) => {
  on('task', {
    extractDocumentXml({ filePath }) {
      return unzipper.Open.file(filePath)
        .then((directory) => {
          const docXml = directory.files.find(f => f.path === 'word/document.xml');
          if (!docXml) throw new Error('document.xml not found in DOCX');
          return docXml.buffer();
        })
        .then((buffer) => buffer.toString('utf8'));
    }
  });
};

cy.task('extractDocumentXml', {
  filePath: 'cypress/downloads/items.docx'
}).then((xml) => {
  // Log or inspect the raw XML content
  cy.log(xml);
  expect(xml).to.include('comment');
});