Snippet to test a custom branch of a TYPO3 extension in e.g. a fork

composer.json

{
  {
    "type":"package",
    "package": {
      "name": "placeholder/for-namespace",
      "type": "typo3-cms-extension",
      "version":"dev-bugfix",
      "source": {
        "url": "https://github.com/your-account/your-repository.git",
        "type": "git",
        "reference": "bugfix"
      }
    }
  },
  require: {
    "placeholder/for-namespace": "dev-bugfix as 9.9.9"
  }
}