feat(*): Add StringExtensionTests

UnitTests/StringExtensionTests.cs

@@ -0,0 +1,29 @@
+using NUnit.Framework;
+using Creek.HelpfulExtensions;
+
+namespace UnitTests
+{
+    public class StringExtensionTests
+    {
+        [SetUp]
+        public void Setup()
+        {
+        }
+
+        [Test]
+        public void IsSubstringBetweenFirst()
+        {
+            string s = "bigfishmandogcatdoghat";
+            s = s.SubstringBetween("fish", "dog");
+            Assert.AreEqual("fishman", s);
+        }
+
+        [Test]
+        public void IsSubstringBetweenLast()
+        {
+            string s = "bigfishmandogcatdoghat";
+            s = s.SubstringBetween("fish", "dog", true);
+            Assert.AreEqual("fishmandogcat", s);
+        }
+    }
+}