public async void ShouldCreateFileCorrectly()
{
var ms = new MemoryStream();
var fileMock = new Mock <IFile>();
fileMock
.Setup(x => x.Create(It.IsAny <string>()))
.Returns(ms);
var fsMock = new Mock <IFileSystem>();
fsMock
.Setup(x => x.File)
.Returns(fileMock.Object);
var fileStore = new FileStore(fsMock.Object, BuildFakeConfiguration());
var id = await fileStore.CreateFile(Convert.FromBase64String("aGVsbG93b3JsZA=="));
id.Should().NotBeEmpty();
Convert.ToBase64String(ms.ToArray()).Should().BeEquivalentTo("aGVsbG93b3JsZA==");
}