public void AddFilter() { var qsb = new QueryStringBuilder(); var key = Guid.NewGuid(); Expression <Func <Person, bool> > exp1 = x => x.Key == key; qsb.AddFilter(exp1); var pattern = $"?$filter=Ref_Key eq guid'{key}'&$format=json"; var result = qsb.Build(); Assert.AreEqual(pattern, result); }