fix: use full path in Directory.SetCurrentDirectory (#1028)

The current directory should always be a rooted path, even if the directory is set to a relative directory.

Author: vbreuss

src/TestableIO.System.IO.Abstractions.TestingHelpers/MockDirectory.cs

@@ -602,7 +602,7 @@ public override void SetCreationTimeUtc(string path, DateTime creationTimeUtc)
         /// <inheritdoc />
         public override void SetCurrentDirectory(string path)
         {
-            currentDirectory = path;
+            currentDirectory = mockFileDataAccessor.Path.GetFullPath(path);
         }
 
         /// <inheritdoc />

tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockDirectoryTests.cs

@@ -1661,6 +1661,17 @@ public void MockDirectory_SetCurrentDirectory_ShouldChangeCurrentDirectory()
             Assert.AreEqual(directory, fileSystem.Directory.GetCurrentDirectory());
         }
 
+        [Test]
+        public void MockDirectory_SetCurrentDirectory_WithRelativePath_ShouldUseFullPath()
+        {
+            var fileSystem = new MockFileSystem();
+            fileSystem.Directory.SetCurrentDirectory(".");
+
+            var result = fileSystem.Directory.GetCurrentDirectory();
+
+            Assert.IsTrue(fileSystem.Path.IsPathRooted(result));
+        }
+
         [Test]
         public void MockDirectory_GetParent_ShouldThrowArgumentNullExceptionIfPathIsNull()
         {