Linked list cycle detection in Golang

linked_list.go

package main

import "fmt"

type listNode struct {
	value int
	next  *listNode
}

func (l *listNode) containsCycle() bool {
	slow, fast := l, l.next
	for fast != nil && fast.next != nil {
		if slow == fast {
			return true
		}

		slow = slow.next
		if fast.next != nil {
			fast = fast.next.next
		}
	}

	return false
}

linked_list_test.go

package main

import "testing"

func TestDetectCycleSingleNode(t *testing.T) {
	l := listNode{value: 0}
	if l.containsCycle() {
		t.Error("single node should not contain cycle")
	}
}

func TestDetectCycleNoCycle(t *testing.T) {
	l1 := &listNode{value: 0}
	l2 := &listNode{value: 1}
	l1.next = l2

	if l1.containsCycle() {
		t.Error("should not contain cycle")
	}
}

func TestDetectCycleSimple(t *testing.T) {
	l1 := &listNode{value: 0}
	l2 := &listNode{value: 1}
	l1.next = l2
	l2.next = l1

	if !l1.containsCycle() {
		t.Error("should contain cycle")
	}
}

func TestDetectCycleLoop(t *testing.T) {
	l1 := &listNode{value: 0}
	l2 := &listNode{value: 1}
	l3 := &listNode{value: 2}
	l4 := &listNode{value: 3}

	l1.next = l2
	l2.next = l3
	l3.next = l4
	l4.next = l1

	if !l1.containsCycle() {
		t.Error("should contain cycle")
	}
}

func TestDetectCycleNineShaped(t *testing.T) {
	l1 := &listNode{value: 0}
	l2 := &listNode{value: 1}
	l3 := &listNode{value: 2}
	l4 := &listNode{value: 3}

	l1.next = l2
	l2.next = l3
	l3.next = l4
	l4.next = l2

	if !l1.containsCycle() {
		t.Error("should contain cycle")
	}
}