Test failure with QuickCheck 2.14.3

[felixonmars]

      Seconds truncate is Nano truncate:                                    FAIL
        *** Failed! Falsified (after 5 tests):
        -1.000000000
        Use --quickcheck-replay=391660 to reproduce.
        Use -p '/Seconds truncate is Nano truncate/' to rerun this test only.

It passes with QuickCheck 2.14.2 or older versions, with everything else unchanged.

[CetinSert]

Please open an issue with QuickCheck and link to this issue there.

[berberman]

I investigated a bit and found that the test "Seconds truncate is Nano truncate" was broken by nick8325/quickcheck@f295094. Previously, arbitrarySizedFractional would generate high precision fractions like -3.0920546619346832e-12, 5.581150636052472e-11, etc. But for now, since the range of denominator is bounded by max 1 n, it's likely that the generated fractions turn out to be integers like -1.00000, 2.00000, etc. However, I found that the test

clock/tests/test.hs

Lines 97 to 100 in 504a3f5

	, QuickCheck.testProperty "Seconds truncate is Nano truncate" $ \(x :: Nano) ->
	let nano = truncate x :: Integer
	seconds = truncate (realToFrac x :: Seconds)
	in nano == seconds

actually fails for all negative integers. For example, let x = -5. According to the definition of properFraction for Seconds:

clock/System/Clock/Seconds.hs

Lines 51 to 54 in 504a3f5

	instance RealFrac Seconds where
	properFraction (Seconds (TimeSpec s ns))
	| s >= 0 = (fromIntegral s, Seconds $ TimeSpec 0 ns)
	| otherwise = (fromIntegral (s+1), Seconds $ TimeSpec (-1) ns)

properFraction (realToFrac x :: Seconds) converts {sec = -5, nsec = 0} to (-4, {sec = -1, nsec = 0}), and then truncate returns the integral part -4, indicating that the integer nearest -5 is -4, instead of -5. Thus, I think this is a bug reveled by the new version of QuickCheck.