add virtual implementation for reading input file

Day.cs

@@ -1,16 +1,23 @@
 using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
 
 namespace aoc2019
 {
     public abstract class Day
     {
         public abstract int DayNumber { get; }
+        public virtual IEnumerable<string> Input =>
+            File.ReadLines($"input/day{DayNumber}.in");
+
         public virtual void AllParts()
         {
             Console.WriteLine($"Day {DayNumber}:");
             Console.WriteLine(Part1());
             Console.WriteLine(Part2());
         }
+
         public abstract string Part1();
         public abstract string Part2();
     }

Day1.cs

@@ -8,8 +8,11 @@ namespace aoc2019
     {
         public override int DayNumber => 1;
 
-        private readonly IEnumerable<int> masses =
-            File.ReadLines("input/day1.in").Select(int.Parse);
+        private readonly IEnumerable<int> masses;
+        public Day1()
+        {
+            masses = Input.Select(int.Parse);
+        }
 
         private static int FuelCost(int weight) => weight / 3 - 2;
         private static int FullCost(int cost)

Day2.cs

@@ -8,8 +8,11 @@ namespace aoc2019
     {
         public override int DayNumber => 2;
 
-        private readonly IEnumerable<int> input =
-            File.ReadLines("input/day2.in").First().Split(',').Select(int.Parse);
+        private readonly IEnumerable<int> input;
+        public Day2()
+        {
+            input = Input.First().Split(',').Select(int.Parse);
+        }
 
         public int RunIntCode(int noun, int verb)
         {

Day3.cs

@@ -14,7 +14,7 @@ namespace aoc2019
 
         public Day3()
         {
-            wires = File.ReadAllLines("input/day3.in").Select(ParseWire).ToList();
+            wires = Input.Select(ParseWire).ToList();
             intersections = wires[0].Keys.Intersect(wires[1].Keys);
         }
 

Day4.cs

@@ -12,9 +12,7 @@ namespace aoc2019
 
         public Day4()
         {
-            var range = File.ReadLines("input/day4.in")
-                .First().Split('-').Select(int.Parse).ToList();
-
+            var range = Input.First().Split('-').Select(int.Parse).ToList();
             start = range[0]; end = range[1];
         }
 

Day5.cs

@@ -8,8 +8,11 @@ namespace aoc2019
     {
         public override int DayNumber => 5;
 
-        private readonly IEnumerable<int> tape =
-            File.ReadLines("input/day5.in").First().Split(',').Select(int.Parse);
+        private readonly IEnumerable<int> tape;
+        public Day5()
+        {
+            tape = Input.First().Split(',').Select(int.Parse);
+        }
 
         private int output;
         public void RunIntCode(List<int> v, int input)