Added explicit tests for the slow StringBuilder based Unidecode implementation that now gets called only for long input strings

Author: carlosirna

test/SlowUnidecoderTest.cs

@@ -0,0 +1,63 @@
+using System;
+using System.Text;
+using Xunit;
+using Unidecode.NET;
+
+namespace Unidecode.NET.Tests
+{
+  // these are the same tests you find in UnidecoderTest, but here we are testing directly the internal function SlowUnidecode
+  // which is the Unidecode implementation that normally gets called only for very long strings
+  // (because it is slower, but it has no limits on the size of the input string)
+  public class SlowUnidecoderTest
+  {
+    [Fact]
+    public void DocTest()
+    {
+      Assert.Equal("Bei Jing ", "\u5317\u4EB0".SlowUnidecode());
+    }
+
+    [Fact]
+    public void CustomTest()
+    {
+      Assert.Equal("Rabota s kirillitsei", "Работа с кириллицей".SlowUnidecode());
+      Assert.Equal("aouoAOUO", "äöűőÄÖŨŐ".SlowUnidecode());
+    }
+
+
+
+    [Fact]
+    public void PythonTest()
+    {
+      
+      Assert.Equal("Hello, World!", "Hello, World!".SlowUnidecode());
+      Assert.Equal("'\"\r\n", "'\"\r\n".SlowUnidecode());
+      Assert.Equal("CZSczs", "ČŽŠčžš".SlowUnidecode());
+      Assert.Equal("a", "ア".SlowUnidecode());
+      Assert.Equal("a", "α".SlowUnidecode());
+      Assert.Equal("a", "а".SlowUnidecode());
+      Assert.Equal("chateau", "ch\u00e2teau".SlowUnidecode());
+      Assert.Equal("vinedos", "vi\u00f1edos".SlowUnidecode());
+    }
+
+    [Fact]
+    public void RussianAlphabetTest()
+    {
+      const string russianAlphabetLowercase = "а б в г д е ё ж з и й к л м н о п р с т у ф х ц ч ш щ ъ ы ь э ю я";
+      const string russianAlphabetUppercase = "А Б В Г Д Е Ё Ж З И Й К Л М Н О П Р С Т У Ф Х Ц Ч Ш Щ Ъ Ы Ь Э Ю Я";
+
+      const string expectedLowercase = "a b v g d e io zh z i i k l m n o p r s t u f kh ts ch sh shch ' y ' e iu ia";
+      const string expectedUppercase = "A B V G D E Io Zh Z I I K L M N O P R S T U F Kh Ts Ch Sh Shch ' Y ' E Iu Ia";
+
+      Assert.Equal(expectedLowercase, russianAlphabetLowercase.SlowUnidecode());
+      Assert.Equal(expectedUppercase, russianAlphabetUppercase.SlowUnidecode());
+    }
+
+
+    [Fact]
+    public void UnidecodeOnNullShouldReturnEmptyString()
+    {
+      Assert.Equal("", ((string)null).SlowUnidecode());
+    }
+
+  }
+}