feat: add options to constructor of MockFileSystem (#1013)

Add a new class `MockFileSystemOptions` and corresponding overloads in the constructor of `MockFileSystem`.
Default values don't change the current behaviour, but when setting `CreateDefaultTempDir` to `false`, the temp directory is not created.

Fixes:
- #983

Author: vbreuss

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

@@ -25,7 +25,21 @@ public MockFileSystem() : this(null) { }
 
         /// <inheritdoc />
         public MockFileSystem(IDictionary<string, MockFileData> files, string currentDirectory = "")
+            : this(files, new MockFileSystemOptions
+            {
+                CurrentDirectory = currentDirectory,
+                CreateDefaultTempDir = true
+            }) { }
+
+        /// <inheritdoc />
+        public MockFileSystem(MockFileSystemOptions options)
+            : this(null, options) { }
+
+        /// <inheritdoc />
+        public MockFileSystem(IDictionary<string, MockFileData> files, MockFileSystemOptions options)
         {
+            options ??= new MockFileSystemOptions();
+            var currentDirectory = options.CurrentDirectory;
             if (string.IsNullOrEmpty(currentDirectory))
             {
                 currentDirectory = XFS.Path(DEFAULT_CURRENT_DIRECTORY);
@@ -63,7 +77,7 @@ public MockFileSystem(IDictionary<string, MockFileData> files, string currentDir
                 AddDirectory(currentDirectory);
             }
 
-            if (!FileExists(defaultTempDirectory))
+            if (options.CreateDefaultTempDir && !FileExists(defaultTempDirectory))
             {
                 AddDirectory(defaultTempDirectory);
             }

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

@@ -0,0 +1,18 @@
+namespace System.IO.Abstractions.TestingHelpers
+{
+    /// <summary>
+    ///     Constructor options for <see cref="MockFileSystem" />
+    /// </summary>
+    public class MockFileSystemOptions
+    {
+        /// <summary>
+        ///     The <see cref="Directory.GetCurrentDirectory()" /> with which the <see cref="MockFileSystem" /> is initialized.
+        /// </summary>
+        public string CurrentDirectory { get; init; } = "";
+
+        /// <summary>
+        /// Flag indicating, if a temporary directory should be created.
+        /// </summary>
+        public bool CreateDefaultTempDir { get; init; } = true;
+    }
+}

src/TestableIO.System.IO.Abstractions.TestingHelpers/TestableIO.System.IO.Abstractions.TestingHelpers.csproj

@@ -15,7 +15,11 @@
             <PrivateAssets>all</PrivateAssets>
             <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
         </PackageReference>
-    </ItemGroup>
+		<PackageReference Include="IsExternalInit" Version="1.0.3">
+			<PrivateAssets>all</PrivateAssets>
+			<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+		</PackageReference>
+	</ItemGroup>
     <ItemGroup>
         <None Include="..\..\images\icon_256x256.png" Pack="true" PackagePath="\" />
     </ItemGroup>

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

@@ -0,0 +1,40 @@
+using NUnit.Framework;
+using XFS = System.IO.Abstractions.TestingHelpers.MockUnixSupport;
+
+namespace System.IO.Abstractions.TestingHelpers.Tests
+{
+    [TestFixture]
+    public class MockFileSystemOptionTests
+    {
+        [Test]
+        [TestCase(true)]
+        [TestCase(false)]
+        public void CreateDefaultTempDir_ShouldBeConsidered(bool createTempDir)
+        {
+            var fileSystem = new MockFileSystem(new MockFileSystemOptions
+            {
+                CreateDefaultTempDir = createTempDir
+            });
+
+            var result = fileSystem.Directory.Exists(fileSystem.Path.GetTempPath());
+
+            Assert.AreEqual(createTempDir, result);
+        }
+
+        [Test]
+        [TestCase(@"C:\path")]
+        [TestCase(@"C:\foo\bar")]
+        public void CurrentDirectory_ShouldBeConsidered(string currentDirectory)
+        {
+            currentDirectory = XFS.Path(currentDirectory);
+            var fileSystem = new MockFileSystem(new MockFileSystemOptions
+            {
+                CurrentDirectory = currentDirectory
+            });
+
+            var result = fileSystem.Directory.GetCurrentDirectory();
+
+            Assert.AreEqual(currentDirectory, result);
+        }
+    }
+}