QueueableとCalloutとTest

CalloutJob.cls

public class CalloutJob implements Queueable, Database.AllowsCallouts {

    public void execute(QueueableContext context) {
        String endpoint = 'https://trust.salesforce.com/';
        HttpRequest req = new HttpRequest();
        req.setMethod('GET');
        req.setEndpoint(endpoint);
        new Http().send(req);
    }

}

CalloutJobTest.cls

@IsTest
private class CalloutJobTest {

    public class CalloutMock implements HttpCalloutMock {
        public HttpResponse respond(HttpRequest req) {
            return new HttpResponse();
        }
    }

    @IsTest
    static void testRunAsAdminUser() {
        Test.setMock(HttpCalloutMock.class, new CalloutMock());

        Test.startTest();
        // runAsの有無は関係ない
        System.runAs([select Id from User where Id = :UserInfo.getUserId()][0]) {
            System.enqueueJob(new CalloutJob());
        }
        // System.CalloutException: Callout loop not allowed
        Test.stopTest();
    }

}