Add extension method and corresponding unit tests to convert (unparse…

src/Nager.PublicSuffix.UnitTest/TldRuleExtensionsTests.cs

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+using System.Linq;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using Nager.PublicSuffix.Extensions;
+using Nager.PublicSuffix.Models;
+using Nager.PublicSuffix.RuleParsers;
+
+namespace Nager.PublicSuffix.UnitTest;
+
+[TestClass]
+public class TldRuleExtensionsTests
+{
+    [TestMethod]
+    public void UnparseWithExceptionTest()
+    {
+        const string rulesInText = """
+                                   foo.com
+                                   !bar.com
+                                   !foo.bar.com
+                                   """;
+
+        var (rules1, rules2) = ParseUnparseRules(rulesInText);
+
+        CollectionAssert.AreEqual(rules1, rules2);
+        Assert.AreEqual(TldRuleType.WildcardException, rules2[1].Type);
+    }
+
+    [TestMethod]
+    public void UnparseWithWildCardTest()
+    {
+        const string rulesInText = """
+                                   natal.br
+                                   net.br
+                                   niteroi.br
+                                   *.nom.br
+                                   not.br
+                                   ntr.br
+                                   odo.br
+                                   ong.br
+                                   org.br
+                                   """;
+        var (rules1, rules2) = ParseUnparseRules(rulesInText);
+
+        CollectionAssert.AreEqual(rules1, rules2);
+        Assert.AreEqual(TldRuleType.Wildcard, rules2[3].Type);
+    }
+
+    private static (TldRule[] rules1, TldRule[] rules2) ParseUnparseRules(string rulesText)
+    {
+        var ruleParser = new TldRuleParser();
+
+        var rules1 = ruleParser.ParseRules(rulesText).ToArray();
+        var rulesUnParsedText = rules1.UnparseRules();
+        var rules2 = ruleParser.ParseRules(rulesUnParsedText).ToArray();
+
+        return (rules1, rules2);
+    }
+}

src/Nager.PublicSuffix/Extensions/TldRuleExtensions.cs

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+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using Nager.PublicSuffix.Models;
+
+namespace Nager.PublicSuffix.Extensions
+{
+    /// <summary>
+    /// TldRule Extensions
+    /// </summary>
+    public static class TldRuleExtensions
+    {
+        /// <summary>
+        /// Converts the collection of <see cref="TldRule"/> <paramref name="rules"/> to text.
+        /// </summary>
+        /// <param name="rules">The collection of <see cref="TldRule"/> rules</param>
+        /// <returns></returns>
+        public static string UnparseRules(this IEnumerable<TldRule> rules)
+        {
+            var rulesData = new StringBuilder();
+            foreach (var division in rules.GroupBy(rule => rule.Division))
+            {
+                switch (division.Key)
+                {
+                    case TldRuleDivision.ICANN:
+                        rulesData.Append("\n// ===BEGIN ICANN DOMAINS===\n");
+                        break;
+                    case TldRuleDivision.Private:
+                        rulesData.Append("\n// ===BEGIN PRIVATE DOMAINS===\n");
+                        break;
+                }
+
+                foreach (var rule in division)
+                {
+                    rulesData.Append("\n");
+
+                    if (rule.Type == TldRuleType.WildcardException)
+                    {
+                        rulesData.Append("!");
+                    }
+                    rulesData.Append(rule.Name);
+                }
+
+                switch (division.Key)
+                {
+                    case TldRuleDivision.ICANN:
+                        rulesData.Append("\n// ===END ICANN DOMAINS===\n");
+                        break;
+                    case TldRuleDivision.Private:
+                        rulesData.Append("\n// ===END PRIVATE DOMAINS===\n");
+                        break;
+                }
+            }
+
+            return rulesData.ToString();
+        }
+    }}