System.Text.EncoderReplacementFallbackBuffer.MovePrevious C# (CSharp) Method

        public override bool MovePrevious()
        {
            // Back up one, only if we just processed the last character (or earlier)
            if (fallbackCount >= -1 && fallbackIndex >= 0)
            {
                fallbackIndex--;
                fallbackCount++;
                return true;
            }

            // Return false 'cause we couldn't do it.
            return false;
        }

        public void FallbackEmptyForEncodingUTF8()
        {
            Buffer b = Encoding.UTF8.EncoderFallback.CreateFallbackBuffer() as Buffer;

            Assert.IsTrue(b.Fallback('X', 0), "#1");
            Assert.IsFalse(b.MovePrevious(), "#2");
            Assert.AreEqual(1, b.Remaining, "#3");
            // the string does not exist.
            Assert.AreEqual('\uFFFD', b.GetNextChar(), "#4");
        }