string to guid extension method; tests

Luticate2.Utils/Utils/LuCoreUtilsExtensions.cs

@@ -8,9 +8,18 @@ namespace Luticate2.Utils.Utils
     {
         public static string ToSnakeCase(this string str)
         {
+            if (str == null)
+            {
+                throw new ArgumentNullException(nameof(str));
+            }
             return string.Concat(str.Select((x, i) => i > 0 && char.IsUpper(x) ? "_" + x.ToString() : x.ToString())).ToLower();
         }
 
+        public static Guid? ToGuid(this string str)
+        {
+            return str == null ? (Guid?)null : new Guid(str);
+        }
+
         public static bool HasProperty(this Type type, string name)
         {
             return type.GetProperty(name) != null;

TestUtils/Utils/LuCoreUtilsExtensionsTest.cs

@@ -0,0 +1,65 @@
+using System;
+using Luticate2.Utils.Utils;
+using Xunit;
+
+namespace TestUtils.Utils
+{
+    public class LuCoreUtilsExtensionsTest
+    {
+        [Fact]
+        public void TestStringToGuidNull()
+        {
+            string str = null;
+            Assert.Null(str.ToGuid());
+        }
+
+        [Fact]
+        public void TestStringToGuidValid()
+        {
+            var str = "365989fc-cbd6-11e6-99ca-3085a902d67c";
+            Assert.Equal(str, str.ToGuid().ToString());
+        }
+
+        [Fact]
+        public void TestStringToGuidInvalid()
+        {
+            var str = "42";
+            Assert.Throws<FormatException>(() => str.ToGuid());
+        }
+
+        [Fact]
+        public void TestStringToSnakeCaseNull()
+        {
+            string str = null;
+            Assert.Throws<ArgumentNullException>(() => str.ToSnakeCase());
+        }
+
+        [Fact]
+        public void TestStringToSnakeCaseEmpty()
+        {
+            var str = "";
+            Assert.Equal("", str.ToSnakeCase());
+        }
+
+        [Fact]
+        public void TestStringToSnakeCase1()
+        {
+            var str = "TestNotEmpty";
+            Assert.Equal("test_not_empty", str.ToSnakeCase());
+        }
+
+        [Fact]
+        public void TestStringToSnakeCase2()
+        {
+            var str = "testNotEmpty";
+            Assert.Equal("test_not_empty", str.ToSnakeCase());
+        }
+
+        [Fact]
+        public void TestStringToSnakeCase3()
+        {
+            var str = "DBContext";
+            Assert.Equal("d_b_context", str.ToSnakeCase());
+        }
+    }
+}