func TestPrependedBlocks(t *testing.T) {
	const BLOCKSIZE = 100
	const BLOCK_COUNT = 20
	checksum := NewFileChecksumGenerator(BLOCKSIZE)

	file1 := io.LimitReader(
		readers.NewNonRepeatingSequence(0),
		BLOCKSIZE*BLOCK_COUNT,
	)

	file2 := io.LimitReader(
		io.MultiReader(
			readers.OneReader(BLOCKSIZE), // Off by one block
			readers.NewNonRepeatingSequence(0),
		),
		BLOCKSIZE*BLOCK_COUNT,
	)

	output1 := bytes.NewBuffer(nil)
	chksum1, _ := checksum.GenerateChecksums(file1, output1)

	output2 := bytes.NewBuffer(nil)
	chksum2, _ := checksum.GenerateChecksums(file2, output2)

	if bytes.Compare(chksum1, chksum2) == 0 {
		t.Fatal("Checksums should be different")
	}

	weaksize, strongSize := checksum.GetChecksumSizes()
	sums1, _ := chunks.LoadChecksumsFromReader(output1, weaksize, strongSize)
	sums2, _ := chunks.LoadChecksumsFromReader(output2, weaksize, strongSize)

	if len(sums1) != len(sums2) {
		t.Fatalf("Checksum lengths differ %v vs %v", len(sums1), len(sums2))
	}

	if sums1[0].Match(sums2[0]) {
		t.Error("Chunk sums1[0] should differ from sums2[0]")
	}

	for i, _ := range sums2 {
		if i == 0 {
			continue
		}

		if !sums1[i-1].Match(sums2[i]) {
			t.Errorf("Chunk sums1[%v] equal sums2[%v]", i-1, i)
		}

	}
}
// Test that partial content that ends in the middle of a strong
// hash is caught correctly
func TestInvalidReaderLength_Strong(t *testing.T) {
	const BLOCKSIZE = 100

	checksum := NewFileChecksumGenerator(BLOCKSIZE)

	file1 := io.LimitReader(
		readers.NewNonRepeatingSequence(0),
		int64(checksum.ChecksumSize())+int64(checksum.WeakRollingHash.Size())+2,
	)

	ws, ss := checksum.GetChecksumSizes()
	r, err := chunks.LoadChecksumsFromReader(file1, ws, ss)

	if r != nil || err != chunks.ErrPartialChecksum {
		t.Error("Expected partial checksum error")
	}
}