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Package quick

import "testing/quick"

Overview ▾

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

The testing/quick package is frozen and is not accepting new features.

func Check

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

A CheckEqualError is the result CheckEqual finding an error.

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

func (*CheckEqualError) Error

func (s *CheckEqualError) Error() string

type CheckError

A CheckError is the result of Check finding an error.

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

func (*CheckError) Error

func (s *CheckError) Error() string

type Config

A Config structure contains options for running a test.

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.
    // A count of zero implies the default, which is usually 100
    // but can be set by the -quickchecks flag.
    MaxCountScale float64
    // Rand specifies a source of random numbers.
    // If nil, a default pseudo-random source will be used.
    Rand *rand.Rand
    // Values specifies a function to generate a slice of
    // arbitrary reflect.Values that are congruent with the
    // arguments to the function being tested.
    // If nil, the top-level Value function is used to generate them.
    Values func([]reflect.Value, *rand.Rand)

type Generator

A Generator can generate random values of its own type.

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

type SetupError

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

type SetupError string

func (SetupError) Error

func (s SetupError) Error() string