public void FilterNumberStartsWithTest() { //Arrange List <Message> messages = new List <Message>(); messages.Add(new Message("+3801", "+38 777", $"Message #1")); messages.Add(new Message("+3802", "+38 777", $"Message #2")); messages.Add(new Message("+3802", "+38 777", $"Message #3")); messages.Add(new Message("+3803", "+38 777", $"Message #4")); messages.Add(new Message("+3802", "+38 777", $"Message #5")); string expectedResult = "+3801"; //Act MessageFilter messageFilter = new MessageFilter(); List <Message> filteredMessages = messageFilter.NumberStartsWith(messages, "+3801"); //Assert Assert.AreEqual(expectedResult, filteredMessages[0].SenderNumber); }