AIO commit

Sorry for the late commit, forgot to commit and push it on Saturday 7th.
Thank god there are moodle reminders

AdventOfCode/AdventOfCode.Test/Day4Test.cs

@@ -0,0 +1,28 @@
+namespace AdventOfCode.Test;
+
+public sealed class Day4Test
+{
+    [Fact]
+    public void Part1()
+    {
+        const string Input = "MMMSXXMASM\nMSAMXMSMSA\nAMXSXMAAMM\nMSAMASMSMX\nXMASAMXAMM\nXXAMMXXAMA\nSMSMSASXSS\nSAXAMASAAA\nMAMMMXMMMM\nMXMXAXMASX";
+        const int Expected = 18;
+        var day4 = new Day4();
+
+        var result = day4.Part1(Input);
+
+        Assert.Equal(Expected, result);
+    }
+    
+    [Fact]
+    public void Part2()
+    {
+        const string Input = ".M.S......\n..A..MSMS.\n.M.S.MAA..\n..A.ASMSM.\n.M.S.M....\n..........\nS.S.S.S.S.\n.A.A.A.A..\nM.M.M.M.M.\n..........";
+        const int Expected = 9;
+        var day4 = new Day4();
+
+        var result = day4.Part2(Input);
+
+        Assert.Equal(Expected, result);
+    }
+}