Added support for DEC r32 instructions (0x48-0x4F) with tests

X86DisassemblerTests/DecInstructionTests.cs

@@ -0,0 +1,68 @@
+namespace X86DisassemblerTests;
+
+using System;
+using Xunit;
+using X86Disassembler.X86;
+
+/// <summary>
+/// Tests for DEC instruction handlers
+/// </summary>
+public class DecInstructionTests
+{
+    /// <summary>
+    /// Tests the DEC EAX instruction (0x48)
+    /// </summary>
+    [Fact]
+    public void TestDecEax()
+    {
+        // Arrange
+        byte[] code = { 0x48 }; // DEC EAX
+        
+        // Act
+        Disassembler disassembler = new Disassembler(code, 0x1000);
+        var instructions = disassembler.Disassemble();
+        
+        // Assert
+        Assert.Single(instructions);
+        Assert.Equal("dec", instructions[0].Mnemonic);
+        Assert.Equal("eax", instructions[0].Operands);
+    }
+    
+    /// <summary>
+    /// Tests the DEC ECX instruction (0x49)
+    /// </summary>
+    [Fact]
+    public void TestDecEcx()
+    {
+        // Arrange
+        byte[] code = { 0x49 }; // DEC ECX
+        
+        // Act
+        Disassembler disassembler = new Disassembler(code, 0x1000);
+        var instructions = disassembler.Disassemble();
+        
+        // Assert
+        Assert.Single(instructions);
+        Assert.Equal("dec", instructions[0].Mnemonic);
+        Assert.Equal("ecx", instructions[0].Operands);
+    }
+    
+    /// <summary>
+    /// Tests the DEC EDI instruction (0x4F)
+    /// </summary>
+    [Fact]
+    public void TestDecEdi()
+    {
+        // Arrange
+        byte[] code = { 0x4F }; // DEC EDI
+        
+        // Act
+        Disassembler disassembler = new Disassembler(code, 0x1000);
+        var instructions = disassembler.Disassemble();
+        
+        // Assert
+        Assert.Single(instructions);
+        Assert.Equal("dec", instructions[0].Mnemonic);
+        Assert.Equal("edi", instructions[0].Operands);
+    }
+}