Added tests for SafeSubstring

Added tests to validate the index and length parameters of the underlying Substring.

Author: jerbri

tests/ServiceStack.Text.Tests/StringExtensionsTests.cs

@@ -226,5 +226,26 @@ public void Can_ParseKeyValueText()
             Assert.That("a:b\nc:d".ParseKeyValueText()["c"], Is.EqualTo("d"));
             Assert.That("a:b\r\nc:d".ParseKeyValueText()["c"], Is.EqualTo("d"));
         }
+        
+        [Test]
+        public void Can_SafeSubstring_with_no_length {
+        
+        	var input = "TestString";
+        	Assert.That(input.SafeSubstring(0), Is.EqualTo("TestString"));
+        	Assert.That(input.SafeSubstring(2), Is.EqualTo("stString"));
+        	Assert.That(input.SafeSubstring(20), Is.EqualTo(""));
+        }
+        
+        [Test]
+        public void Can_SafeSubstring_with_length {
+        	var input = "TestString";
+        	Assert.That(input.SafeSubstring(0,4), Is.EqualTo("Test"));
+        	Assert.That(input.SafeSubstring(2,4), Is.EqualTo("stSt"));
+        	Assert.That(input.SafeSubstring(20,4), Is.EqualTo(""));
+        	Assert.That(input.SafeSubstring(0,20), Is.EqualTo("TestString"));
+        	
+        }
+        }
+        }
 	}
-}
+}