feat: make CommandRunner a singleton

EasyCLI/CommandRunner/CommandRunner.cs

@@ -7,11 +7,32 @@ namespace EasyCLI.CommandRunner;
 /// </summary>
 public sealed class CommandRunner
 {
+    /// <summary>
+    /// Contains the singleton instance of the CommandRunner.
+    /// </summary>
+    private static CommandRunner? _instance;
+
+    /// <summary>
+    /// Makes the constructor private to prevent instantiation outside of the class.
+    /// </summary>
+    private CommandRunner()
+    {
+    }
+
     /// <summary>
     /// Gets the collection of commands registered with the CommandRunner.
     /// </summary>
     public List<Command> Commands { get; } = new();
 
+    /// <summary>
+    /// Gets the singleton instance of the CommandRunner. If the instance does not exist, it is created.
+    /// </summary>
+    /// <returns>CommandRunner instance</returns>
+    public static CommandRunner GetInstance()
+    {
+        return _instance ??= new CommandRunner();
+    }
+
     /// <summary>
     /// Registers a command with the CommandRunner.
     /// </summary>

EasySave.Tests/EasyCLI/CommandRunnerTests/CommandRunnerTests.cs

@@ -9,21 +9,21 @@ public class CommandRunnerTests
     public void RegisterCommand_ShouldAddCommandToCommands()
     {
         // Arrange
-        var commandRunner = new CommandRunner();
+        var commandRunner = CommandRunner.GetInstance();
         var command = new Mock<MockCommand>();
 
         // Act
         commandRunner.RegisterCommand(command.Object);
 
         // Assert
-        commandRunner.Commands.Should().Contain(command.Object);
+        CommandRunner.GetInstance().Commands.Should().Contain(command.Object);
     }
 
     [Fact]
     public void RunWithArgs_ShouldReturnFalse_WhenNoCommandMatches()
     {
         // Arrange
-        var commandRunner = new CommandRunner();
+        var commandRunner = CommandRunner.GetInstance();
         var args = new List<string> { "command" };
 
         // Act
@@ -55,7 +55,7 @@ public void RunWithArgs_ShouldCallRun_WhenCommandMatches()
     public void GetCommandFromArgs_ShouldReturnNull_WhenNoCommandMatches()
     {
         // Arrange
-        var commandRunner = new CommandRunner();
+        var commandRunner = CommandRunner.GetInstance();
         var args = new List<string> { "command" };
 
         // Act