Queueable インターフェースの実装サンプルです。(テストクラスでエラーでてます。。)

01_QueueableDemo.page

<apex:page controller="QueueableDemoController" showHeader="true" sidebar="false">
    <apex:form id="form">
        <apex:pageBlock title="Queueable Demo">
            <apex:commandButton value="Execute!!" action="{!doExecute}" reRender="form" />
            &nbsp;
            <apex:commandButton value="Refresh!!" action="{!doRefresh}" reRender="form" />
        </apex:pageBlock>
        <apex:pageBlock title="{!$ObjectType.AsyncApexJob.Label}" rendered="{!jobInfos.size > 0}">
            <apex:pageBlockTable value="{!jobInfos}" var="item">
                <apex:column headerValue="{!$ObjectType.AsyncApexJob.Fields.Id.Label}">
                    <apex:outputField value="{!item.Id}" />
                </apex:column>
                <apex:column headerValue="{!$ObjectType.AsyncApexJob.Fields.Status.Label}">
                    <apex:outputField value="{!item.Status}" />
                </apex:column>
                <apex:column headerValue="{!$ObjectType.AsyncApexJob.Fields.NumberOfErrors.Label}">
                    <apex:outputField value="{!item.NumberOfErrors}" />
                </apex:column>
            </apex:pageBlockTable>
        </apex:pageBlock>
    </apex:form>
</apex:page>

02_QueueableDemoController.cls

public with sharing class QueueableDemoController {
    
    public List<AsyncApexJob> jobInfos {get; set;}
    private Id jobID = null;
    
    public QueueableDemoController() {
        this.jobInfos = new List<AsyncApexJob>();
    }
    
    public void doExecute() {
        this.jobID = System.enqueueJob(new AsyncExecutionExample());
        if (String.isNotEmpty(this.jobID)) {
            this.jobInfos = getAsyncApexJob(this.jobID);
        }
    }
    
    public void doRefresh() {
        if (String.isNotEmpty(this.jobID)) {
            this.jobInfos = getAsyncApexJob(this.jobID);
        }
    }
    
    private List<AsyncApexJob> getAsyncApexJob(Id jobID) {
        return [SELECT Status,NumberOfErrors FROM AsyncApexJob WHERE Id=:jobID];
    }
}

03_QueueableDemoControllerTest.cls

@isTest
private class QueueableDemoControllerTest {
    
    static testMethod void QueueableDemoControllerTest() {
        
        Test.startTest();
        
        QueueableDemoController cls = new QueueableDemoController();
        cls.doExecute();
        System.assertEquals(cls.jobInfos.isEmpty(), true);
        
        Test.stopTest();
        
        cls.doRefresh();
        System.assertEquals(cls.jobInfos.isEmpty(), false);
    }
}

04_AsyncExecutionExample.cls

public with sharing class AsyncExecutionExample implements Queueable {
    
    public void execute(QueueableContext context) {
        Account a = new Account(Name='Acme',Phone='(415) 555-1212');
        insert a;
    }
}

05_AsyncExecutionExampleTest.cls

@isTest
public class AsyncExecutionExampleTest {
    
    static testmethod void test1() {
        // startTest/stopTest block to force async processes
        // to run in the test.
        Test.startTest();
            ID jobID = System.enqueueJob(new AsyncExecutionExample());
        Test.stopTest();
        // Validate that the job has run
        AsyncApexJob jobInfo = [SELECT Status,NumberOfErrors FROM AsyncApexJob WHERE Id=:jobID];
        System.assertEquals('Completed', jobInfo.Status);
    }