Feature/4442 directory and combinedfilepath

src/Cake.Common.Tests/Unit/IO/Paths/ConvertableFilePathTests.cs

@@ -2,10 +2,14 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System;
 using System.Diagnostics.CodeAnalysis;
+using System.IO;
 using Cake.Common.IO.Paths;
 using Cake.Core.IO;
+using NSubstitute;
 using Xunit;
+using Xunit.v3;
 
 namespace Cake.Common.Tests.Unit.IO.Paths
 {
@@ -70,6 +74,65 @@ public void Should_Return_Null_If_Convertable_Directory_Path_Is_Null()
                     // Then
                     Assert.Null(result);
                 }
+
+                [Fact]
+                [SuppressMessage("ReSharper", "ExpressionIsAlwaysNull")]
+                public void Should_Return_Null_Exception_If_Convertable_Directory_Path_Is_Null()
+                {
+                    // Given
+                    DirectoryPath dirPath = null;
+
+                    // When
+                    var filePath = new ConvertableFilePath("file.txt");
+                    // Then
+                    var ex = Assert.Throws<ArgumentNullException>(() => (dirPath + filePath).ToString());
+                }
+
+                [Fact]
+                [SuppressMessage("ReSharper", "ExpressionIsAlwaysNull")]
+                public void Should_Return_Null_Exception_If_Convertable_FilePath_Is_Null()
+                {
+                    // Given
+                    DirectoryPath dirPath = new DirectoryPath("X");
+
+                    // When
+                    ConvertableFilePath filePath = null;
+                    // Then
+                    var ex = Assert.Throws<ArgumentNullException>(() => (dirPath + filePath).ToString());
+                }
+
+                [Fact]
+                [SuppressMessage("ReSharper", "ExpressionIsAlwaysNull")]
+                public void Should_Return_Combined_Directorypath_FilePath_Including_Separator()
+                {
+                    // Given
+                    DirectoryPath dirPath = new DirectoryPath("X");
+                    var filePath = new ConvertableFilePath("file.txt");
+
+                    // When
+                    var result = (dirPath + filePath).ToString();
+
+                    // Then
+                    Assert.Equal("X/file.txt", result);
+                }
+
+                [Fact]
+                [SuppressMessage("ReSharper", "ExpressionIsAlwaysNull")]
+                public void Should_Return_Combined_RootPath_Directorypath_FilePath_Including_Separator()
+                {
+                    // Given
+                    var contextcake = Substitute.For<Core.ICakeContext>();
+
+                    DirectoryPath dirPath = new ConvertableDirectoryPath(new DirectoryPath("X"));
+                    var filePath = new ConvertableFilePath(new FilePath("file.txt"));
+                    var rootdir = new ConvertableDirectoryPath(new DirectoryPath(".."));
+
+                    // When
+                    var result = (rootdir + dirPath + filePath).ToString();
+
+                    // Then
+                    Assert.Equal("../X/file.txt", result);
+                }
             }
 
             public sealed class ConvertToString

src/Cake.Common/IO/Paths/ConvertableFilePath.cs

@@ -61,5 +61,26 @@ public override string ToString()
         {
             return Path.FullPath;
         }
+
+        /// <summary>
+        /// Combines the directory path and file path with the separator.
+        /// </summary>
+        /// <param name="dir">DirectoryPath.</param>
+        /// <param name="file">ConvertableFilePath.</param>
+        /// <returns>
+        /// A <see cref="System.String" /> that represents this instance.
+        /// </returns>
+        public static string operator +(DirectoryPath dir, ConvertableFilePath file)
+        {
+            if (dir == null)
+            {
+                throw new ArgumentNullException(nameof(dir));
+            }
+            if (file == null)
+            {
+                throw new ArgumentNullException(nameof(file));
+            }
+            return string.Concat(dir.FullPath, dir.Separator.ToString(), file);
+        }
     }
 }