fix: MockFile - clone the bytes in read/write allbytes methods (#856)

Author: jamesmoore

src/System.IO.Abstractions.TestingHelpers/MockFile.cs

@@ -538,7 +538,7 @@ public override byte[] ReadAllBytes(string path)
                 throw CommonExceptions.FileNotFound(path);
             }
             mockFileDataAccessor.GetFile(path).CheckFileAccess(path, FileAccess.Read);
-            return mockFileDataAccessor.GetFile(path).Contents;
+            return mockFileDataAccessor.GetFile(path).Contents.ToArray();
         }
 
         /// <inheritdoc />
@@ -784,7 +784,7 @@ public override void WriteAllBytes(string path, byte[] bytes)
             mockFileDataAccessor.PathVerifier.IsLegalAbsoluteOrRelative(path, "path");
             VerifyDirectoryExists(path);
 
-            mockFileDataAccessor.AddFile(path, new MockFileData(bytes));
+            mockFileDataAccessor.AddFile(path, new MockFileData(bytes.ToArray()));
         }
 
         /// <summary>

tests/System.IO.Abstractions.TestingHelpers.Tests/MockFileReadAllBytesTests.cs

@@ -62,6 +62,28 @@ public void MockFile_ReadAllBytes_ShouldTolerateAltDirectorySeparatorInPath()
 
             Assert.AreEqual(data, fileSystem.File.ReadAllBytes(altPath));
         }
+
+        [Test]
+        public void MockFile_ReadAllBytes_ShouldReturnANewCopyOfTheFileContents()
+        {
+            var path = XFS.Path(@"c:\something\demo.bin");
+            var fileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
+            {
+                { path, new MockFileData(new byte[] { 1, 2, 3, 4 }) }
+            });
+
+            var firstRead = fileSystem.File.ReadAllBytes(path);
+
+            var secondRead = fileSystem.File.ReadAllBytes(path);
+
+            for (int i = 0; i < firstRead.Length; i++)
+            {
+                firstRead[i] += 1;
+            }
+
+            Assert.AreNotEqual(firstRead, secondRead);
+        }
+
 #if FEATURE_ASYNC_FILE
         [Test]
         public async Task MockFile_ReadAllBytesAsync_ShouldReturnOriginalByteData()

tests/System.IO.Abstractions.TestingHelpers.Tests/MockFileWriteAllBytesTests.cs

@@ -83,6 +83,27 @@ public void MockFile_WriteAllBytes_ShouldThrowAnArgumentNullExceptionIfBytesAreN
             Assert.That(exception.ParamName, Is.EqualTo("bytes"));
         }
 
+        [Test]
+        public void MockFile_WriteAllBytes_ShouldWriteASeparateCopyToTheFileSystem()
+        {
+            var fileSystem = new MockFileSystem();
+            string path = XFS.Path(@"c:\something\file.bin");
+            fileSystem.AddDirectory(XFS.Path(@"c:\something"));
+            var fileContent = new byte[] { 1, 2, 3, 4 };
+
+            fileSystem.File.WriteAllBytes(path, fileContent);
+
+            for(int i = 0; i < fileContent.Length; i++)
+            {
+                fileContent[i] += 1;
+            }
+
+            var readAgain = fileSystem.File.ReadAllBytes(path);
+
+            Assert.AreNotEqual(fileContent, readAgain);
+        }
+
+
 #if FEATURE_ASYNC_FILE
         [Test]
         public void MockFile_WriteAllBytesAsync_ShouldThrowDirectoryNotFoundExceptionIfPathDoesNotExists()