smallcheck-1.1: A property-based testing library

Maintainer Roman Cheplyaka Safe

Test.SmallCheck

Description

This module exports the main pieces of SmallCheck functionality.

To generate test cases for your own types, refer to Test.SmallCheck.Series.

For pointers to other sources of information about SmallCheck, please refer to the README at https://github.com/feuerbach/smallcheck/blob/master/README.md

Synopsis

# Constructing tests

The simplest kind of test is a function (possibly of many arguments) returning `Bool`. The function arguments are interpreted as being universally, existentially or uniquely quantified, depending on the quantification context.

The default quantification context is universal (`forAll`).

`forAll`, `exists` and `existsUnique` functions set the quantification context for function arguments. Depending on the quantification context, the test `\x y -> p x y` may be equivalent to:

• ∀ x, y. p x y (`forAll`)
• ∃ x, y: p x y (`exists`)
• ∃! x, y: p x y (`existsUnique`)

The quantification context affects all the variables immediately following the quantification operator, also extending past `over`, `changeDepth` and `changeDepth1` functions.

However, it doesn't extend past other functions, like `monadic`, and doesn't affect the operands of `==>`. Such functions start a fresh default quantification context.

## Examples

• `\x y -> p x y` means ∀ x, y. p x y
• `exists \$ \x y -> p x y` means ∃ x, y: p x y
• `exists \$ \x -> forAll \$ \y -> p x y` means ∃ x: ∀ y. p x y
• `existsUnique \$ \x y -> p x y` means ∃! (x, y): p x y
• `existsUnique \$ \x -> over s \$ \y -> p x y` means ∃! (x, y): y ∈ s && p x y
• `existsUnique \$ \x -> monadic \$ \y -> p x y` means ∃! x: ∀ y. [p x y]
• `existsUnique \$ \x -> existsUnique \$ \y -> p x y` means ∃! x: ∃! y: p x y
• `exists \$ \x -> (\y -> p y) ==> (\z -> q z)` means ∃ x: (∀ y. p y) => (∀ z. p z)

forAll :: Testable m a => a -> Property mSource

Set the universal quantification context

exists :: Testable m a => a -> Property mSource

Set the existential quantification context

existsUnique :: Testable m a => a -> Property mSource

Set the uniqueness quantification context.

Bear in mind that ∃! (x, y): p x y is not the same as ∃! x: ∃! y: p x y.

For example, ∃! x: ∃! y: |x| = |y| is true (it holds only when x=0), but ∃! (x,y): |x| = |y| is false (there are many such pairs).

As is customary in mathematics, `existsUnique \$ \x y -> p x y` is equivalent to `existsUnique \$ \(x,y) -> p x y` and not to `existsUnique \$ \x -> existsUnique \$ \y -> p x y` (the latter, of course, may be explicitly written when desired).

That is, all the variables affected by the same uniqueness context are quantified simultaneously as a tuple.

over :: (Show a, Testable m b) => Series m a -> (a -> b) -> Property mSource

`over s \$ \x -> p x` makes `x` range over the `Series` `s` (by default, all variables range over the `series` for their types).

Note that, unlike the quantification operators, this affects only the variable following the operator and not subsequent variables.

`over` does not affect the quantification context.

monadic :: Testable m a => m a -> Property mSource

Execute a monadic test

(==>) :: (Testable m c, Testable m a) => c -> a -> Property mSource

The `==>` operator can be used to express a restricting condition under which a property should hold. It corresponds to implication in the classical logic.

Note that `==>` resets the quantification context for its operands to the default (universal).

changeDepth :: Testable m a => (Depth -> Depth) -> a -> Property mSource

Run property with a modified depth. Affects all quantified variables in the property.

changeDepth1 :: (Show a, Serial m a, Testable m b) => (Depth -> Depth) -> (a -> b) -> Property mSource

Quantify the function's argument over its `series`, but adjust the depth. This doesn't affect any subsequent variables.

# Running tests

`smallCheck` is a simple way to run a test.

As an alternative, consider using the `test-framework` package: http://hackage.haskell.org/package/test-framework

It allows to organize SmallCheck properties into a test suite (possibly together with HUnit or QuickCheck tests), apply timeouts, get nice statistics etc.

To use SmallCheck properties with test-framework, install the `test-framework-smallcheck` package: http://hackage.haskell.org/package/test-framework

For more ways to run the tests, see Test.SmallCheck.Drivers.

type Depth = IntSource

Maximum depth of generated test values.

For data values, it is the depth of nested constructor applications.

For functional values, it is both the depth of nested case analysis and the depth of results.

smallCheck :: Testable IO a => Depth -> a -> IO ()Source

A simple driver that runs the test in the `IO` monad and prints the results.

# Main types and classes

class Monad m => Testable m a Source

Class of tests that can be run in a monad. For pure tests, it is recommended to keep their types polymorphic in `m` rather than specialising it to `Identity`.

Instances

 Monad m => Testable m Bool (Monad m, ~ (* -> *) m n) => Testable n (Property m) (Serial m a, Show a, Testable m b) => Testable m (a -> b) Monad m => Testable m (Either Reason Reason) Works like the `Bool` instance, but includes an explanation of the result. `Left` and `Right` correspond to test failure and success respectively.

data Property m Source

The type of properties over the monad `m`

Instances

 (Monad m, ~ (* -> *) m n) => Testable n (Property m) Typeable1 m => Typeable (Property m)

type Reason = StringSource

An explanation for the test outcome