public async Task FileBufferingReadStream_AsyncReadOverThreshold_CreatesFile()
        {
            var    inner = MakeStream(1024 * 2);
            string tempFileName;

            using (var stream = new FileBufferingReadStream(inner, 1024, null, GetCurrentDirectory()))
            {
                var bytes = new byte[1000];
                var read0 = await stream.ReadAsync(bytes, 0, bytes.Length);

                Assert.Equal(bytes.Length, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read1 = await stream.ReadAsync(bytes, 0, bytes.Length);

                Assert.Equal(bytes.Length, read1);
                Assert.Equal(read0 + read1, stream.Length);
                Assert.Equal(read0 + read1, stream.Position);
                Assert.False(stream.InMemory);
                Assert.NotNull(stream.TempFileName);
                tempFileName = stream.TempFileName;
                Assert.True(File.Exists(tempFileName));

                var read2 = await stream.ReadAsync(bytes, 0, bytes.Length);

                Assert.Equal(inner.Length - read0 - read1, read2);
                Assert.Equal(read0 + read1 + read2, stream.Length);
                Assert.Equal(read0 + read1 + read2, stream.Position);
                Assert.False(stream.InMemory);
                Assert.NotNull(stream.TempFileName);
                Assert.True(File.Exists(tempFileName));

                var read3 = await stream.ReadAsync(bytes, 0, bytes.Length);

                Assert.Equal(0, read3);
            }

            Assert.False(File.Exists(tempFileName));
        }
        public async Task FileBufferingReadStream_AsyncReadWithInMemoryLimit_EnforcesLimit()
        {
            var inner = MakeStream(1024 * 2);

            using (var stream = new FileBufferingReadStream(inner, 1024, 900, Directory.GetCurrentDirectory()))
            {
                var bytes = new byte[500];
                var read0 = await stream.ReadAsync(bytes, 0, bytes.Length);

                Assert.Equal(bytes.Length, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var exception = await Assert.ThrowsAsync <IOException>(() => stream.ReadAsync(bytes, 0, bytes.Length));

                Assert.Equal("Buffer limit exceeded.", exception.Message);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);
                Assert.False(File.Exists(stream.TempFileName));
            }
        }
        public async Task FileBufferingReadStream_AsyncReadUnderThreshold_DoesntCreateFile()
        {
            var inner = MakeStream(1024 * 2);

            using (var stream = new FileBufferingReadStream(inner, 1024 * 3, null, Directory.GetCurrentDirectory()))
            {
                var bytes = new byte[1000];
                var read0 = await stream.ReadAsync(bytes, 0, bytes.Length);

                Assert.Equal(bytes.Length, read0);
                Assert.Equal(read0, stream.Length);
                Assert.Equal(read0, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read1 = await stream.ReadAsync(bytes, 0, bytes.Length);

                Assert.Equal(bytes.Length, read1);
                Assert.Equal(read0 + read1, stream.Length);
                Assert.Equal(read0 + read1, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read2 = await stream.ReadAsync(bytes, 0, bytes.Length);

                Assert.Equal(inner.Length - read0 - read1, read2);
                Assert.Equal(read0 + read1 + read2, stream.Length);
                Assert.Equal(read0 + read1 + read2, stream.Position);
                Assert.True(stream.InMemory);
                Assert.Null(stream.TempFileName);

                var read3 = await stream.ReadAsync(bytes, 0, bytes.Length);

                Assert.Equal(0, read3);
            }
        }