// Copyright 2019 Gregory Petrosyan <gregory.petrosyan@gmail.com>//// This Source Code Form is subject to the terms of the Mozilla Public// License, v. 2.0. If a copy of the MPL was not distributed with this// file, You can obtain one at https://mozilla.org/MPL/2.0/. package rapid_test import (	"testing" 	"pgregory.net/rapid") // Queue implements integer queue with a fixed maximum size.type Queue struct {	buf []int	in  int	out int} func NewQueue(n int) *Queue {	return &Queue{		buf: make([]int, n+1),	}} // Precondition: Size() > 0.func (q *Queue) Get() int {	i := q.buf[q.out]	q.out = (q.out + 1) % len(q.buf)	return i} // Precondition: Size() < n.func (q *Queue) Put(i int) {	q.buf[q.in] = i	q.in = (q.in + 1) % len(q.buf)} func (q *Queue) Size() int {	return (q.in - q.out) % len(q.buf)} func testQueue(t *rapid.T) {	n := rapid.IntRange(1, 1000).Draw(t, "n") // maximum queue size	q := NewQueue(n)                          // queue being tested	var state []int                           // model of the queue 	t.Repeat(		rapid.SampledFrom([]rapid.StateMachineAction{			{				Name: "get",				Func: func(t *rapid.T) {					if q.Size() == 0 {						t.Skip("queue empty")					} 					i := q.Get()					if i != state[0] {						t.Fatalf("got invalid value: %v vs expected %v", i, state[0])					}					state = state[1:]				},			},			{				Name: "put",				Func: func(t *rapid.T) {					if q.Size() == n {						t.Skip("queue full")					} 					i := rapid.Int().Draw(t, "i")					q.Put(i)					state = append(state, i)				},			},		}), 		func(t *rapid.T) {			if q.Size() != len(state) {				t.Fatalf("queue size mismatch: %v vs expected %v", q.Size(), len(state))			}		},	)} // Rename to TestQueue(t *testing.T) to make an actual (failing) test.func ExampleT_Repeat_queue() {	var t *testing.T	rapid.Check(t, testQueue)}