test_js_fetch.js

  function mockWithType(contentType, httpMethod = "GET", referenceUrl = "/") {
    const urlResult = baseUrl + referenceUrl

    console.log("Mocked '" + urlResult + "' for " + httpMethod);
    fetchMock.mock(
      (url, opts) => {
        return url === urlResult && opts && opts.headers && opts.headers.get('Content-Type') === contentType
      },
      {
        number: 200,
        body: {}
      },
      {
        method: httpMethod
      }
    )
  }