Run Format

Package quick

import "testing/quick"

Overview ▾

Package quick implements utility functions to help with black box testing.

func Check

func Check(f interface{}, config *Config) (err error)

Check looks for an input to f, any function that returns bool, such that f returns false. It calls f repeatedly, with arbitrary values for each argument. If f returns false on a given input, Check returns that input as a *CheckError. For example:

func TestOddMultipleOfThree(t *testing.T) {
	f := func(x int) bool {
		y := OddMultipleOfThree(x)
		return y%2 == 1 && y%3 == 0
	if err := quick.Check(f, nil); err != nil {

func CheckEqual

func CheckEqual(f, g interface{}, config *Config) (err error)

CheckEqual looks for an input on which f and g return different results. It calls f and g repeatedly with arbitrary values for each argument. If f and g return different answers, CheckEqual returns a *CheckEqualError describing the input and the outputs.

func Value

func Value(t reflect.Type, rand *rand.Rand) (value reflect.Value, ok bool)

Value returns an arbitrary value of the given type. If the type implements the Generator interface, that will be used. Note: To create arbitrary values for structs, all the fields must be exported.

type CheckEqualError

type CheckEqualError struct {
    Out1 []interface{}
    Out2 []interface{}

A CheckEqualError is the result CheckEqual finding an error.

func (*CheckEqualError) Error

func (s *CheckEqualError) Error() string

type CheckError

type CheckError struct {
    Count int
    In    []interface{}

A CheckError is the result of Check finding an error.

func (*CheckError) Error

func (s *CheckError) Error() string

type Config

type Config struct {
    // MaxCount sets the maximum number of iterations. If zero,
    // MaxCountScale is used.
    MaxCount int
    // MaxCountScale is a non-negative scale factor applied to the default
    // maximum. If zero, the default is unchanged.
    MaxCountScale float64
    // If non-nil, rand is a source of random numbers. Otherwise a default
    // pseudo-random source will be used.
    Rand *rand.Rand
    // If non-nil, the Values function generates a slice of arbitrary
    // reflect.Values that are congruent with the arguments to the function
    // being tested. Otherwise, the top-level Values function is used
    // to generate them.
    Values func([]reflect.Value, *rand.Rand)

A Config structure contains options for running a test.

type Generator

type Generator interface {
    // Generate returns a random instance of the type on which it is a
    // method using the size as a size hint.
    Generate(rand *rand.Rand, size int) reflect.Value

A Generator can generate random values of its own type.

type SetupError

type SetupError string

A SetupError is the result of an error in the way that check is being used, independent of the functions being tested.

func (SetupError) Error

func (s SetupError) Error() string