quickcheck

QuickCheck is a property-based testing framework originally developed for the Haskell programming language. It enables automated testing by letting developers specify properties that should hold for a function or system under test across a wide range of inputs, rather than writing individual test cases. QuickCheck then automatically generates random inputs to exercise those properties and reports any failures.

The core idea is to separate observing inputs from verifying outcomes. A property is a statement that should be true for all valid inputs. QuickCheck provides mechanisms to generate diverse test data and to shrink failing input examples to simpler counterexamples, making failures easier to understand. If a property holds for many randomized trials, confidence in the property's validity increases; if a counterexample is found, shrinking helps reveal the smallest input that breaks the property.

Since its introduction, QuickCheck has influenced a broad family of property-based testing tools and has inspired numerous language ports and similar frameworks. Notable translations or inspired projects include implementations for languages such as Scala, F#, Erlang, and others. The approach has become popular for testing invariants, refactoring safety, and catching edge cases that may be missed by example-based tests.

Common examples of properties include statements like: reversing a list twice yields the original list, or sorting a list preserves its length and contains the same elements. While powerful, property-based testing does not prove correctness; it complements traditional tests and requires thoughtful design of properties and data generators to be effective.