function warn(oLogMock, sExpectedWarning, vDetails) {
		return oLogMock.expects(`warning`)
			// do not construct arguments in vain!
			.exactly(Log.isLoggable(Log.Level.WARNING, sComponent) ? 1 : 0)
			.withExactArgs(_matchArg(sExpectedWarning), _matchArg(vDetails), sComponent);
	}
Expects a warning with the given message for the given log mock.

@param {object} oLogMock
  mock for <code>sap.base.log</code>
@param {string} sExpectedWarning
  expected warning message
@param {any} [vDetails]
  expected warning details
@returns {object}
  the resulting Sinon expectation