Ensure files end with a single new line

closes #464

Src/CSharpier.Tests/DocPrinterTests.cs

@@ -677,6 +677,25 @@ public void Align_Should_Convert_Non_Trailing_Spaces_To_Tabs()
             PrintedDocShouldBe(doc, $"+ + 1{NewLine}\t\t  2", useTabs: true);
         }
 
+        [TestCase(0, "\n")]
+        [TestCase(0, "\r\n")]
+        [TestCase(1, "\r\n")]
+        [TestCase(1, "\r\n")]
+        [TestCase(2, "\r\n")]
+        [TestCase(2, "\r\n")]
+        public void Print_Should_Include_Single_NewLine(int instances, string endOfLine)
+        {
+            var doc = "1";
+            for (var x = 0; x < instances; x++)
+            {
+                doc += endOfLine;
+            }
+
+            var result = DocPrinter.DocPrinter.Print(doc, new PrinterOptions(), endOfLine);
+
+            result.Should().Be($"1{endOfLine}");
+        }
+
         [Test]
         public void Scratch()
         {

Src/CSharpier.Tests/FormattingTests/TestFiles/AttributeLists.cst

@@ -100,4 +100,3 @@ class ClassName
     AnotherAttribute
 ]
 public class ClassName { }
-

Src/CSharpier.Tests/FormattingTests/TestFiles/Comments.cst

@@ -89,5 +89,3 @@ public class ClassName
     // regular comment does not cause breaking
     IReadOnlyList<IArgument> ICommand.Arguments => Arguments;
 }
-
-

Src/CSharpier.Tests/FormattingTests/TestFiles/EnumDeclarations.cst

@@ -11,4 +11,3 @@ public enum E
     B = A,
     C = 2 + A
 }
-

Src/CSharpier.Tests/FormattingTests/TestFiles/UsingStatements.cst

@@ -68,4 +68,3 @@ class ClassName
         }
     }
 }
-

Src/CSharpier/DocPrinter/DocPrinter.cs

@@ -42,10 +42,7 @@ public string Print()
                 ProcessNextCommand();
             }
 
-            if (Output.Length == 0 || Output[^1] != '\n')
-            {
-                Output.Append(EndOfLine);
-            }
+            EnsureOutputEndsWithSingleNewLine();
 
             var result = Output.ToString();
             if (PrinterOptions.TrimInitialLines)
@@ -56,6 +53,21 @@ public string Print()
             return result;
         }
 
+        private void EnsureOutputEndsWithSingleNewLine()
+        {
+            var trimmed = 0;
+            for (; trimmed < Output.Length; trimmed++)
+            {
+                if (Output[^(trimmed + 1)] != '\r' && Output[^(trimmed + 1)] != '\n')
+                {
+                    break;
+                }
+            }
+            Output.Length -= trimmed;
+
+            Output.Append(EndOfLine);
+        }
+
         private void ProcessNextCommand()
         {
             var (indent, mode, doc) = RemainingCommands.Pop();