Issue with custom moduleNameMapper for Jest

[ferrannp]

In an internal project I try to add a new rule in my package.json like:

"jest": {
  moduleNameMapper": {
    "\\.(html)$": "<rootDir>/fileMock.js"
  }
}

I see the property gets properly merge but my test keeps failing. I tried directly in test.js, if I do it like:

  moduleNameMapper['\\.(html)$'] = `${TEST_MOCKS_PATH}/fileMock.js`;
  // We map webpack aliases from webpack-isomorphic-tools-config file
  // so Jest can detect them in tests too
  Object.keys(aliases).forEach((key) => {
    moduleNameMapper[`^${key}(.*)$`] = `${aliases[key]}$1`;
  });

My test passes. However, if I place it right after like:

  // We map webpack aliases from webpack-isomorphic-tools-config file
  // so Jest can detect them in tests too
  Object.keys(aliases).forEach((key) => {
    moduleNameMapper[`^${key}(.*)$`] = `${aliases[key]}$1`;
  });

  moduleNameMapper['\\.(html)$'] = `${TEST_MOCKS_PATH}/fileMock.js`;

Then my test fails. The order should not matter so I am wondering if html is hitting another rule under aliases.