nick8325 / nick8325/quickcheck
Generate edge cases
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- Dominant language
- Haskell
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- Merged PRs (30d)
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Description
Generate edge cases (minBound, maxBound, minBound + 1, ...) with some low frequency.
abs always returns a positive number right?
>>> quickCheck (\(n :: Int) -> abs n >= 0)
+++ OK, passed 100 tests.
Alright let's ship it — well — the test fails if we run it on Int8s often enough
>>> quickCheck (\(n :: Int8) -> abs n >= 0)
+++ OK, passed 100 tests.
>>> quickCheck (\(n :: Int8) -> abs n >= 0)
+++ OK, passed 100 tests.
>>> quickCheck (\(n :: Int8) -> abs n >= 0)
+++ OK, passed 100 tests.
>>> quickCheck (\(n :: Int8) -> abs n >= 0)
*** Failed! Falsifiable (after 23 tests):
-128
Turns out it doesn't actually hold for Ints
>>> abs @Int minBound
-9223372036854775808
This could be detected for larger sample spaces like Int if minBound were generated. I would like to see this in the Arbitrary Int instance but maybe a modifier is better?
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First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by examining QuickCheck's Arbitrary Int generation, then compare the proposed instance change with a modifier approach. Reproduce the Int8 and Int minBound examples from the issue and determine how low-frequency boundary generation should be specified; done means larger sample spaces can reliably expose these edge cases without making ordinary tests impractical.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- haskell
- Domain
- testing-qa
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100