fix: pass on FileAccess to open function when FileMode is Create or CreateNew. (#714)

Author: willson556

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

@@ -126,9 +126,9 @@ public override Stream Create(string path, int bufferSize) =>
             Create(path, bufferSize, FileOptions.None);
 
         public override Stream Create(string path, int bufferSize, FileOptions options) =>
-            CreateInternal(path, options);
+            CreateInternal(path, FileAccess.Write, options);
 
-        private Stream CreateInternal(string path, FileOptions options)
+        private Stream CreateInternal(string path, FileAccess access, FileOptions options)
         {
             if (path == null)
             {
@@ -140,7 +140,7 @@ private Stream CreateInternal(string path, FileOptions options)
 
             var mockFileData = new MockFileData(new byte[0]);
             mockFileDataAccessor.AddFile(path, mockFileData);
-            return OpenWriteInternal(path, options);
+            return OpenInternal(path, FileMode.Open, access, options);
         }
 
         public override StreamWriter CreateText(string path)
@@ -442,13 +442,13 @@ private Stream OpenInternal(
 
             if (!exists || mode == FileMode.CreateNew)
             {
-                return Create(path);
+                return CreateInternal(path, access, options);
             }
 
             if (mode == FileMode.Create || mode == FileMode.Truncate)
             {
                 Delete(path);
-                return Create(path);
+                return CreateInternal(path, access, options);
             }
 
             var mockFileData = mockFileDataAccessor.GetFile(path);

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

@@ -51,6 +51,19 @@ public void MockFile_Open_CreatesNewFileFileOnCreate()
             Assert.That(stream.Length, Is.EqualTo(0));
         }
 
+        [Test]
+        public void MockFile_Open_AllowsReadWriteOnCreate()
+        {
+            string filepath = XFS.Path(@"c:\something\doesnt\exist.txt");
+            var filesystem = new MockFileSystem(new Dictionary<string, MockFileData>());
+            filesystem.AddDirectory(XFS.Path(@"c:\something\doesnt"));
+
+            var stream = filesystem.File.Open(filepath, FileMode.Create);
+
+            Assert.True(stream.CanRead);
+            Assert.True(stream.CanWrite);
+        }
+
         [Test]
         public void MockFile_Open_CreatesNewFileFileOnCreateNew()
         {