2 files changed, 712 insertions, 0 deletions
diff --git a/src/testing/quick/quick.go b/src/testing/quick/quick.go
new file mode 100644
index 0000000..d711742
--- /dev/null
+++ b/src/testing/quick/quick.go
@@ -0,0 +1,385 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package quick implements utility functions to help with black box testing.
+//
+// The testing/quick package is frozen and is not accepting new features.
+package quick
+
+import (
+	"flag"
+	"fmt"
+	"math"
+	"math/rand"
+	"reflect"
+	"strings"
+	"time"
+)
+
+var defaultMaxCount *int = flag.Int("quickchecks", 100, "The default number of iterations for each check")
+
+// 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
+}
+
+// randFloat32 generates a random float taking the full range of a float32.
+func randFloat32(rand *rand.Rand) float32 {
+	f := rand.Float64() * math.MaxFloat32
+	if rand.Int()&1 == 1 {
+		f = -f
+	}
+	return float32(f)
+}
+
+// randFloat64 generates a random float taking the full range of a float64.
+func randFloat64(rand *rand.Rand) float64 {
+	f := rand.Float64() * math.MaxFloat64
+	if rand.Int()&1 == 1 {
+		f = -f
+	}
+	return f
+}
+
+// randInt64 returns a random int64.
+func randInt64(rand *rand.Rand) int64 {
+	return int64(rand.Uint64())
+}
+
+// complexSize is the maximum length of arbitrary values that contain other
+// values.
+const complexSize = 50
+
+// 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.
+func Value(t reflect.Type, rand *rand.Rand) (value reflect.Value, ok bool) {
+	return sizedValue(t, rand, complexSize)
+}
+
+// sizedValue returns an arbitrary value of the given type. The size
+// hint is used for shrinking as a function of indirection level so
+// that recursive data structures will terminate.
+func sizedValue(t reflect.Type, rand *rand.Rand, size int) (value reflect.Value, ok bool) {
+	if m, ok := reflect.Zero(t).Interface().(Generator); ok {
+		return m.Generate(rand, size), true
+	}
+
+	v := reflect.New(t).Elem()
+	switch concrete := t; concrete.Kind() {
+	case reflect.Bool:
+		v.SetBool(rand.Int()&1 == 0)
+	case reflect.Float32:
+		v.SetFloat(float64(randFloat32(rand)))
+	case reflect.Float64:
+		v.SetFloat(randFloat64(rand))
+	case reflect.Complex64:
+		v.SetComplex(complex(float64(randFloat32(rand)), float64(randFloat32(rand))))
+	case reflect.Complex128:
+		v.SetComplex(complex(randFloat64(rand), randFloat64(rand)))
+	case reflect.Int16:
+		v.SetInt(randInt64(rand))
+	case reflect.Int32:
+		v.SetInt(randInt64(rand))
+	case reflect.Int64:
+		v.SetInt(randInt64(rand))
+	case reflect.Int8:
+		v.SetInt(randInt64(rand))
+	case reflect.Int:
+		v.SetInt(randInt64(rand))
+	case reflect.Uint16:
+		v.SetUint(uint64(randInt64(rand)))
+	case reflect.Uint32:
+		v.SetUint(uint64(randInt64(rand)))
+	case reflect.Uint64:
+		v.SetUint(uint64(randInt64(rand)))
+	case reflect.Uint8:
+		v.SetUint(uint64(randInt64(rand)))
+	case reflect.Uint:
+		v.SetUint(uint64(randInt64(rand)))
+	case reflect.Uintptr:
+		v.SetUint(uint64(randInt64(rand)))
+	case reflect.Map:
+		numElems := rand.Intn(size)
+		v.Set(reflect.MakeMap(concrete))
+		for i := 0; i < numElems; i++ {
+			key, ok1 := sizedValue(concrete.Key(), rand, size)
+			value, ok2 := sizedValue(concrete.Elem(), rand, size)
+			if !ok1 || !ok2 {
+				return reflect.Value{}, false
+			}
+			v.SetMapIndex(key, value)
+		}
+	case reflect.Pointer:
+		if rand.Intn(size) == 0 {
+			v.SetZero() // Generate nil pointer.
+		} else {
+			elem, ok := sizedValue(concrete.Elem(), rand, size)
+			if !ok {
+				return reflect.Value{}, false
+			}
+			v.Set(reflect.New(concrete.Elem()))
+			v.Elem().Set(elem)
+		}
+	case reflect.Slice:
+		numElems := rand.Intn(size)
+		sizeLeft := size - numElems
+		v.Set(reflect.MakeSlice(concrete, numElems, numElems))
+		for i := 0; i < numElems; i++ {
+			elem, ok := sizedValue(concrete.Elem(), rand, sizeLeft)
+			if !ok {
+				return reflect.Value{}, false
+			}
+			v.Index(i).Set(elem)
+		}
+	case reflect.Array:
+		for i := 0; i < v.Len(); i++ {
+			elem, ok := sizedValue(concrete.Elem(), rand, size)
+			if !ok {
+				return reflect.Value{}, false
+			}
+			v.Index(i).Set(elem)
+		}
+	case reflect.String:
+		numChars := rand.Intn(complexSize)
+		codePoints := make([]rune, numChars)
+		for i := 0; i < numChars; i++ {
+			codePoints[i] = rune(rand.Intn(0x10ffff))
+		}
+		v.SetString(string(codePoints))
+	case reflect.Struct:
+		n := v.NumField()
+		// Divide sizeLeft evenly among the struct fields.
+		sizeLeft := size
+		if n > sizeLeft {
+			sizeLeft = 1
+		} else if n > 0 {
+			sizeLeft /= n
+		}
+		for i := 0; i < n; i++ {
+			elem, ok := sizedValue(concrete.Field(i).Type, rand, sizeLeft)
+			if !ok {
+				return reflect.Value{}, false
+			}
+			v.Field(i).Set(elem)
+		}
+	default:
+		return reflect.Value{}, false
+	}
+
+	return v, true
+}
+
+// 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)
+}
+
+var defaultConfig Config
+
+// getRand returns the *rand.Rand to use for a given Config.
+func (c *Config) getRand() *rand.Rand {
+	if c.Rand == nil {
+		return rand.New(rand.NewSource(time.Now().UnixNano()))
+	}
+	return c.Rand
+}
+
+// getMaxCount returns the maximum number of iterations to run for a given
+// Config.
+func (c *Config) getMaxCount() (maxCount int) {
+	maxCount = c.MaxCount
+	if maxCount == 0 {
+		if c.MaxCountScale != 0 {
+			maxCount = int(c.MaxCountScale * float64(*defaultMaxCount))
+		} else {
+			maxCount = *defaultMaxCount
+		}
+	}
+
+	return
+}
+
+// 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 (s SetupError) Error() string { return string(s) }
+
+// A CheckError is the result of Check finding an error.
+type CheckError struct {
+	Count int
+	In    []any
+}
+
+func (s *CheckError) Error() string {
+	return fmt.Sprintf("#%d: failed on input %s", s.Count, toString(s.In))
+}
+
+// A CheckEqualError is the result CheckEqual finding an error.
+type CheckEqualError struct {
+	CheckError
+	Out1 []any
+	Out2 []any
+}
+
+func (s *CheckEqualError) Error() string {
+	return fmt.Sprintf("#%d: failed on input %s. Output 1: %s. Output 2: %s", s.Count, toString(s.In), toString(s.Out1), toString(s.Out2))
+}
+
+// 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 {
+//			t.Error(err)
+//		}
+//	}
+func Check(f any, config *Config) error {
+	if config == nil {
+		config = &defaultConfig
+	}
+
+	fVal, fType, ok := functionAndType(f)
+	if !ok {
+		return SetupError("argument is not a function")
+	}
+
+	if fType.NumOut() != 1 {
+		return SetupError("function does not return one value")
+	}
+	if fType.Out(0).Kind() != reflect.Bool {
+		return SetupError("function does not return a bool")
+	}
+
+	arguments := make([]reflect.Value, fType.NumIn())
+	rand := config.getRand()
+	maxCount := config.getMaxCount()
+
+	for i := 0; i < maxCount; i++ {
+		err := arbitraryValues(arguments, fType, config, rand)
+		if err != nil {
+			return err
+		}
+
+		if !fVal.Call(arguments)[0].Bool() {
+			return &CheckError{i + 1, toInterfaces(arguments)}
+		}
+	}
+
+	return nil
+}
+
+// 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 CheckEqual(f, g any, config *Config) error {
+	if config == nil {
+		config = &defaultConfig
+	}
+
+	x, xType, ok := functionAndType(f)
+	if !ok {
+		return SetupError("f is not a function")
+	}
+	y, yType, ok := functionAndType(g)
+	if !ok {
+		return SetupError("g is not a function")
+	}
+
+	if xType != yType {
+		return SetupError("functions have different types")
+	}
+
+	arguments := make([]reflect.Value, xType.NumIn())
+	rand := config.getRand()
+	maxCount := config.getMaxCount()
+
+	for i := 0; i < maxCount; i++ {
+		err := arbitraryValues(arguments, xType, config, rand)
+		if err != nil {
+			return err
+		}
+
+		xOut := toInterfaces(x.Call(arguments))
+		yOut := toInterfaces(y.Call(arguments))
+
+		if !reflect.DeepEqual(xOut, yOut) {
+			return &CheckEqualError{CheckError{i + 1, toInterfaces(arguments)}, xOut, yOut}
+		}
+	}
+
+	return nil
+}
+
+// arbitraryValues writes Values to args such that args contains Values
+// suitable for calling f.
+func arbitraryValues(args []reflect.Value, f reflect.Type, config *Config, rand *rand.Rand) (err error) {
+	if config.Values != nil {
+		config.Values(args, rand)
+		return
+	}
+
+	for j := 0; j < len(args); j++ {
+		var ok bool
+		args[j], ok = Value(f.In(j), rand)
+		if !ok {
+			err = SetupError(fmt.Sprintf("cannot create arbitrary value of type %s for argument %d", f.In(j), j))
+			return
+		}
+	}
+
+	return
+}
+
+func functionAndType(f any) (v reflect.Value, t reflect.Type, ok bool) {
+	v = reflect.ValueOf(f)
+	ok = v.Kind() == reflect.Func
+	if !ok {
+		return
+	}
+	t = v.Type()
+	return
+}
+
+func toInterfaces(values []reflect.Value) []any {
+	ret := make([]any, len(values))
+	for i, v := range values {
+		ret[i] = v.Interface()
+	}
+	return ret
+}
+
+func toString(interfaces []any) string {
+	s := make([]string, len(interfaces))
+	for i, v := range interfaces {
+		s[i] = fmt.Sprintf("%#v", v)
+	}
+	return strings.Join(s, ", ")
+}
diff --git a/src/testing/quick/quick_test.go b/src/testing/quick/quick_test.go
new file mode 100644
index 0000000..9df6dd4
--- /dev/null
+++ b/src/testing/quick/quick_test.go
@@ -0,0 +1,327 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package quick
+
+import (
+	"math/rand"
+	"reflect"
+	"testing"
+)
+
+func fArray(a [4]byte) [4]byte { return a }
+
+type TestArrayAlias [4]byte
+
+func fArrayAlias(a TestArrayAlias) TestArrayAlias { return a }
+
+func fBool(a bool) bool { return a }
+
+type TestBoolAlias bool
+
+func fBoolAlias(a TestBoolAlias) TestBoolAlias { return a }
+
+func fFloat32(a float32) float32 { return a }
+
+type TestFloat32Alias float32
+
+func fFloat32Alias(a TestFloat32Alias) TestFloat32Alias { return a }
+
+func fFloat64(a float64) float64 { return a }
+
+type TestFloat64Alias float64
+
+func fFloat64Alias(a TestFloat64Alias) TestFloat64Alias { return a }
+
+func fComplex64(a complex64) complex64 { return a }
+
+type TestComplex64Alias complex64
+
+func fComplex64Alias(a TestComplex64Alias) TestComplex64Alias { return a }
+
+func fComplex128(a complex128) complex128 { return a }
+
+type TestComplex128Alias complex128
+
+func fComplex128Alias(a TestComplex128Alias) TestComplex128Alias { return a }
+
+func fInt16(a int16) int16 { return a }
+
+type TestInt16Alias int16
+
+func fInt16Alias(a TestInt16Alias) TestInt16Alias { return a }
+
+func fInt32(a int32) int32 { return a }
+
+type TestInt32Alias int32
+
+func fInt32Alias(a TestInt32Alias) TestInt32Alias { return a }
+
+func fInt64(a int64) int64 { return a }
+
+type TestInt64Alias int64
+
+func fInt64Alias(a TestInt64Alias) TestInt64Alias { return a }
+
+func fInt8(a int8) int8 { return a }
+
+type TestInt8Alias int8
+
+func fInt8Alias(a TestInt8Alias) TestInt8Alias { return a }
+
+func fInt(a int) int { return a }
+
+type TestIntAlias int
+
+func fIntAlias(a TestIntAlias) TestIntAlias { return a }
+
+func fMap(a map[int]int) map[int]int { return a }
+
+type TestMapAlias map[int]int
+
+func fMapAlias(a TestMapAlias) TestMapAlias { return a }
+
+func fPtr(a *int) *int {
+	if a == nil {
+		return nil
+	}
+	b := *a
+	return &b
+}
+
+type TestPtrAlias *int
+
+func fPtrAlias(a TestPtrAlias) TestPtrAlias { return a }
+
+func fSlice(a []byte) []byte { return a }
+
+type TestSliceAlias []byte
+
+func fSliceAlias(a TestSliceAlias) TestSliceAlias { return a }
+
+func fString(a string) string { return a }
+
+type TestStringAlias string
+
+func fStringAlias(a TestStringAlias) TestStringAlias { return a }
+
+type TestStruct struct {
+	A int
+	B string
+}
+
+func fStruct(a TestStruct) TestStruct { return a }
+
+type TestStructAlias TestStruct
+
+func fStructAlias(a TestStructAlias) TestStructAlias { return a }
+
+func fUint16(a uint16) uint16 { return a }
+
+type TestUint16Alias uint16
+
+func fUint16Alias(a TestUint16Alias) TestUint16Alias { return a }
+
+func fUint32(a uint32) uint32 { return a }
+
+type TestUint32Alias uint32
+
+func fUint32Alias(a TestUint32Alias) TestUint32Alias { return a }
+
+func fUint64(a uint64) uint64 { return a }
+
+type TestUint64Alias uint64
+
+func fUint64Alias(a TestUint64Alias) TestUint64Alias { return a }
+
+func fUint8(a uint8) uint8 { return a }
+
+type TestUint8Alias uint8
+
+func fUint8Alias(a TestUint8Alias) TestUint8Alias { return a }
+
+func fUint(a uint) uint { return a }
+
+type TestUintAlias uint
+
+func fUintAlias(a TestUintAlias) TestUintAlias { return a }
+
+func fUintptr(a uintptr) uintptr { return a }
+
+type TestUintptrAlias uintptr
+
+func fUintptrAlias(a TestUintptrAlias) TestUintptrAlias { return a }
+
+func reportError(property string, err error, t *testing.T) {
+	if err != nil {
+		t.Errorf("%s: %s", property, err)
+	}
+}
+
+func TestCheckEqual(t *testing.T) {
+	reportError("fArray", CheckEqual(fArray, fArray, nil), t)
+	reportError("fArrayAlias", CheckEqual(fArrayAlias, fArrayAlias, nil), t)
+	reportError("fBool", CheckEqual(fBool, fBool, nil), t)
+	reportError("fBoolAlias", CheckEqual(fBoolAlias, fBoolAlias, nil), t)
+	reportError("fFloat32", CheckEqual(fFloat32, fFloat32, nil), t)
+	reportError("fFloat32Alias", CheckEqual(fFloat32Alias, fFloat32Alias, nil), t)
+	reportError("fFloat64", CheckEqual(fFloat64, fFloat64, nil), t)
+	reportError("fFloat64Alias", CheckEqual(fFloat64Alias, fFloat64Alias, nil), t)
+	reportError("fComplex64", CheckEqual(fComplex64, fComplex64, nil), t)
+	reportError("fComplex64Alias", CheckEqual(fComplex64Alias, fComplex64Alias, nil), t)
+	reportError("fComplex128", CheckEqual(fComplex128, fComplex128, nil), t)
+	reportError("fComplex128Alias", CheckEqual(fComplex128Alias, fComplex128Alias, nil), t)
+	reportError("fInt16", CheckEqual(fInt16, fInt16, nil), t)
+	reportError("fInt16Alias", CheckEqual(fInt16Alias, fInt16Alias, nil), t)
+	reportError("fInt32", CheckEqual(fInt32, fInt32, nil), t)
+	reportError("fInt32Alias", CheckEqual(fInt32Alias, fInt32Alias, nil), t)
+	reportError("fInt64", CheckEqual(fInt64, fInt64, nil), t)
+	reportError("fInt64Alias", CheckEqual(fInt64Alias, fInt64Alias, nil), t)
+	reportError("fInt8", CheckEqual(fInt8, fInt8, nil), t)
+	reportError("fInt8Alias", CheckEqual(fInt8Alias, fInt8Alias, nil), t)
+	reportError("fInt", CheckEqual(fInt, fInt, nil), t)
+	reportError("fIntAlias", CheckEqual(fIntAlias, fIntAlias, nil), t)
+	reportError("fInt32", CheckEqual(fInt32, fInt32, nil), t)
+	reportError("fInt32Alias", CheckEqual(fInt32Alias, fInt32Alias, nil), t)
+	reportError("fMap", CheckEqual(fMap, fMap, nil), t)
+	reportError("fMapAlias", CheckEqual(fMapAlias, fMapAlias, nil), t)
+	reportError("fPtr", CheckEqual(fPtr, fPtr, nil), t)
+	reportError("fPtrAlias", CheckEqual(fPtrAlias, fPtrAlias, nil), t)
+	reportError("fSlice", CheckEqual(fSlice, fSlice, nil), t)
+	reportError("fSliceAlias", CheckEqual(fSliceAlias, fSliceAlias, nil), t)
+	reportError("fString", CheckEqual(fString, fString, nil), t)
+	reportError("fStringAlias", CheckEqual(fStringAlias, fStringAlias, nil), t)
+	reportError("fStruct", CheckEqual(fStruct, fStruct, nil), t)
+	reportError("fStructAlias", CheckEqual(fStructAlias, fStructAlias, nil), t)
+	reportError("fUint16", CheckEqual(fUint16, fUint16, nil), t)
+	reportError("fUint16Alias", CheckEqual(fUint16Alias, fUint16Alias, nil), t)
+	reportError("fUint32", CheckEqual(fUint32, fUint32, nil), t)
+	reportError("fUint32Alias", CheckEqual(fUint32Alias, fUint32Alias, nil), t)
+	reportError("fUint64", CheckEqual(fUint64, fUint64, nil), t)
+	reportError("fUint64Alias", CheckEqual(fUint64Alias, fUint64Alias, nil), t)
+	reportError("fUint8", CheckEqual(fUint8, fUint8, nil), t)
+	reportError("fUint8Alias", CheckEqual(fUint8Alias, fUint8Alias, nil), t)
+	reportError("fUint", CheckEqual(fUint, fUint, nil), t)
+	reportError("fUintAlias", CheckEqual(fUintAlias, fUintAlias, nil), t)
+	reportError("fUintptr", CheckEqual(fUintptr, fUintptr, nil), t)
+	reportError("fUintptrAlias", CheckEqual(fUintptrAlias, fUintptrAlias, nil), t)
+}
+
+// This tests that ArbitraryValue is working by checking that all the arbitrary
+// values of type MyStruct have x = 42.
+type myStruct struct {
+	x int
+}
+
+func (m myStruct) Generate(r *rand.Rand, _ int) reflect.Value {
+	return reflect.ValueOf(myStruct{x: 42})
+}
+
+func myStructProperty(in myStruct) bool { return in.x == 42 }
+
+func TestCheckProperty(t *testing.T) {
+	reportError("myStructProperty", Check(myStructProperty, nil), t)
+}
+
+func TestFailure(t *testing.T) {
+	f := func(x int) bool { return false }
+	err := Check(f, nil)
+	if err == nil {
+		t.Errorf("Check didn't return an error")
+	}
+	if _, ok := err.(*CheckError); !ok {
+		t.Errorf("Error was not a CheckError: %s", err)
+	}
+
+	err = CheckEqual(fUint, fUint32, nil)
+	if err == nil {
+		t.Errorf("#1 CheckEqual didn't return an error")
+	}
+	if _, ok := err.(SetupError); !ok {
+		t.Errorf("#1 Error was not a SetupError: %s", err)
+	}
+
+	err = CheckEqual(func(x, y int) {}, func(x int) {}, nil)
+	if err == nil {
+		t.Errorf("#2 CheckEqual didn't return an error")
+	}
+	if _, ok := err.(SetupError); !ok {
+		t.Errorf("#2 Error was not a SetupError: %s", err)
+	}
+
+	err = CheckEqual(func(x int) int { return 0 }, func(x int) int32 { return 0 }, nil)
+	if err == nil {
+		t.Errorf("#3 CheckEqual didn't return an error")
+	}
+	if _, ok := err.(SetupError); !ok {
+		t.Errorf("#3 Error was not a SetupError: %s", err)
+	}
+}
+
+// Recursive data structures didn't terminate.
+// Issues 8818 and 11148.
+func TestRecursive(t *testing.T) {
+	type R struct {
+		Ptr      *R
+		SliceP   []*R
+		Slice    []R
+		Map      map[int]R
+		MapP     map[int]*R
+		MapR     map[*R]*R
+		SliceMap []map[int]R
+	}
+
+	f := func(r R) bool { return true }
+	Check(f, nil)
+}
+
+func TestEmptyStruct(t *testing.T) {
+	f := func(struct{}) bool { return true }
+	Check(f, nil)
+}
+
+type (
+	A struct{ B *B }
+	B struct{ A *A }
+)
+
+func TestMutuallyRecursive(t *testing.T) {
+	f := func(a A) bool { return true }
+	Check(f, nil)
+}
+
+// Some serialization formats (e.g. encoding/pem) cannot distinguish
+// between a nil and an empty map or slice, so avoid generating the
+// zero value for these.
+func TestNonZeroSliceAndMap(t *testing.T) {
+	type Q struct {
+		M map[int]int
+		S []int
+	}
+	f := func(q Q) bool {
+		return q.M != nil && q.S != nil
+	}
+	err := Check(f, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+
+func TestInt64(t *testing.T) {
+	var lo, hi int64
+	f := func(x int64) bool {
+		if x < lo {
+			lo = x
+		}
+		if x > hi {
+			hi = x
+		}
+		return true
+	}
+	cfg := &Config{MaxCount: 10000}
+	Check(f, cfg)
+	if uint64(lo)>>62 == 0 || uint64(hi)>>62 == 0 {
+		t.Errorf("int64 returned range %#016x,%#016x; does not look like full range", lo, hi)
+	}
+}