function addResponse(vResponse) {
				if (Array.isArray(vResponse)) {
					vResponse.forEach(addResponse);
				} else if (vResponse.source) {
					let oPromise = mSource2Promise.get(vResponse.source);
					if (!oPromise) {
						oPromise = fetch(sBase + vResponse.source)
							.then((oResponse) => oResponse.text());
						mSource2Promise.set(vResponse.source, oPromise);
					}
					oPromise.then((sMessage) => {
						vResponse.message = sMessage;
						vResponse.headers ??= {};
						vResponse.headers["Content-Type"] ||= contentType(vResponse.source);
						delete vResponse.source;
					}, () => { /* Caller is responsible for error handling, see Promise.all */ });
				}
			}
Gets a Promise that resolves if all sources have been loaded asynchronously.
The <code>message</code> property of the response object is set with the source's content
and the <code>source</code> property is deleted from the response object.

@param {map} mFixture
  The fixture for {@link sap.ui.test.TestUtils.useFakeServer}; it is modified during the
  call
@param {object[]} [aRegExps]
  The regular expression array for {@link sap.ui.test.TestUtils.useFakeServer}; it is
  modified during the call
@param {string} [sBase="sap/ui/core/qunit/odata/v4/data"]
  The base path for {@link sap.ui.test.TestUtils.useFakeServer}
@returns {Promise}
  A Promise that resolves with <code>undefined</code> when all sources are loaded;
  rejects with an error if at least one source cannot be loaded

@public