Tests for LazyByteString invariants are missing

[sjakobi]

bytestring/Data/ByteString/Lazy/Internal.hs

Lines 161 to 175 in 3b0f5d3

	-- | The data type invariant:
	-- Every ByteString is either 'Empty' or consists of non-null 'S.ByteString's.
	-- All functions must preserve this, and the QC properties must check this.
	--
	invariant :: ByteString -> Bool
	invariant Empty = True
	invariant (Chunk (S.BS _ len) cs) = len > 0 && invariant cs
	-- | In a form that checks the invariant lazily.
	checkInvariant :: ByteString -> ByteString
	checkInvariant Empty = Empty
	checkInvariant (Chunk c@(S.BS _ len) cs)
	| len > 0 = Chunk c (checkInvariant cs)
	| otherwise = error $ "Data.ByteString.Lazy: invariant violation:"
	++ show (Chunk c cs)

Despite the comment about QC properties, there seem to be no tests that apply invariant or checkInvariant to the output of LazyByteString-producing functions.