fix: initialization of UnixFileMode (#662)

* Fix initialization of `UnixFileMode`
* Add tests

Author: vbreuss

Source/Testably.Abstractions.Testing/Storage/InMemoryContainer.cs

@@ -92,7 +92,10 @@ public IFileSystemExtensibility Extensibility
 
 #if FEATURE_FILESYSTEM_UNIXFILEMODE
 	/// <inheritdoc cref="IStorageContainer.UnixFileMode" />
-	public UnixFileMode UnixFileMode { get; set; } = (UnixFileMode)(-1);
+	public UnixFileMode UnixFileMode { get; set; } = UnixFileMode.OtherRead |
+	                                                 UnixFileMode.GroupRead |
+	                                                 UnixFileMode.UserWrite |
+	                                                 UnixFileMode.UserRead;
 #endif
 
 	/// <inheritdoc cref="IStorageContainer.AppendBytes(byte[])" />

Tests/Testably.Abstractions.Tests/FileSystem/File/UnixFileModeTests.cs

@@ -8,6 +8,26 @@ public abstract partial class UnixFileModeTests<TFileSystem>
 	: FileSystemTestBase<TFileSystem>
 	where TFileSystem : IFileSystem
 {
+	[SkippableTheory]
+	[AutoData]
+	public void GetUnixFileMode_ShouldBeInitializedCorrectly(
+		string path)
+	{
+		Skip.If(Test.RunsOnWindows);
+		
+		FileSystem.File.WriteAllText(path, "");
+		UnixFileMode expected = UnixFileMode.OtherRead |
+		                        UnixFileMode.GroupRead |
+		                        UnixFileMode.UserWrite |
+		                        UnixFileMode.UserRead;
+
+		#pragma warning disable CA1416
+		UnixFileMode result = FileSystem.File.GetUnixFileMode(path);
+		#pragma warning restore CA1416
+
+		result.Should().Be(expected);
+	}
+
 	[SkippableTheory]
 	[AutoData]
 	public void GetUnixFileMode_ShouldThrowPlatformNotSupportedException_OnWindows(

Tests/Testably.Abstractions.Tests/FileSystem/FileSystemInfo/UnixFileModeTests.cs

@@ -40,12 +40,15 @@ public void UnixFileMode_SetterShouldThrowPlatformNotSupportedException_OnWindow
 
 	[SkippableTheory]
 	[AutoData]
-	public void UnixFileMode_ShouldBeInitializedToMinusOne(
+	public void UnixFileMode_ShouldBeInitializedCorrectly(
 		string path)
 	{
-		Skip.IfNot(Test.RunsOnWindows);
+		Skip.If(Test.RunsOnWindows);
 
-		UnixFileMode expected = (UnixFileMode)(-1);
+		UnixFileMode expected = UnixFileMode.OtherRead |
+		                        UnixFileMode.GroupRead |
+		                        UnixFileMode.UserWrite |
+		                        UnixFileMode.UserRead;
 		FileSystem.File.WriteAllText(path, "some content");
 		IFileInfo fileSystemInfo = FileSystem.FileInfo.New(path);