How do I effectively test asynchronous Apex in Salesforce?
Testing asynchronous Apex in Salesforce requires a slightly different approach compared to testing synchronous code. Asynchronous Apex includes any process that runs outside the main transaction, such as @future methods, Batch Apex, Queueable Apex, and Scheduled Apex. Because these processes are executed asynchronously by the Salesforce system, there is no guarantee of exactly when they will run. This makes testing more complex, since by default, asynchronous processes do not execute immediately within a unit test context.
Salesforce provides a built-in mechanism to handle this situation through the use of Test.startTest() and Test.stopTest(). The purpose of these methods is to ensure that any asynchronous calls made between them are executed synchronously during test execution.
Here is a simple example:
@isTest
private class AsyncTestExample {
@isTest static void testFutureMethod() {
Account acc = new Account(Name = 'Test Account');
insert acc;
Test.startTest();
AsyncUtil.executeFutureMethod(acc.Id);
Test.stopTest();
Account updatedAcc = [SELECT Id, Description FROM Account WHERE Id = :acc.Id];
System.assertEquals('Processed asynchronously', updatedAcc.Description);
}
}
Code Explanation:
This test creates a new Account record as test data. The test then starts a new test context with Test.startTest() to isolate governor limits and prepare for asynchronous execution. It calls a hypothetical future method executeFutureMethod, which will run asynchronously. When Test.stopTest() is called, Salesforce forces execution of all asynchronous jobs queued since startTest(). The test then queries the updated Account and asserts that the asynchronous processing updated the Description field as expected.
A key limitation arises when testing nested asynchronous processes. For instance, if a scheduled Apex job enqueues a batch job, the batch will not run during the unit test. Consider the example below:
public class MySchedulable implements Schedulable {
private Account a;
public MySchedulable(Account a) {
this.a = a;
}
public void execute(SchedulableContext sc) {
a.Description = 'Contacted the customer';
update a;
Database.executeBatch(new ContactsUpdaterBatch(a), 200);
}
}
public class ContactsUpdaterBatch implements Database.Batchable<sObject> {
public Database.QueryLocator start(Database.BatchableContext bc) {
return Database.getQueryLocator([SELECT Id FROM Contact WHERE AccountId = :a.Id]);
}
public void execute(Database.BatchableContext bc, List<Contact> scope) {
for(Contact c : scope) {
c.Description = 'Account has been contacted';
}
update scope;
}
public void finish(Database.BatchableContext bc) {}
}
Code Explanation:
The MySchedulable class implements the Schedulable interface, allowing it to be executed as a scheduled job. It accepts an Account record and updates its Description field. Then, it enqueues a batch job ContactsUpdaterBatch to process related Contact records. The batch job implements Database.Batchable, with start providing the query to fetch Contacts, execute updating the records, and finish left empty. This illustrates multi-layer asynchronous behavior, which has special considerations in testing.
The following test will fail for the nested batch:
@isTest
public static void testSchedulableAndBatch() {
Account a = [SELECT Id FROM Account LIMIT 1];
Test.startTest();
System.schedule('TEST_MySchedulable', '0 0 * * * ?', new MySchedulable(a));
Test.stopTest();
a = [SELECT Id, Description, (SELECT Id, Description FROM Contacts) FROM Account WHERE Id = :a.Id];
System.assertEquals('Contacted the customer', a.Description);
for (Contact c : a.Contacts) {
System.assertEquals('Account has been contacted', c.Description);
}
}
Code Explanation:
This test queries an Account record to use in scheduling the job. Between Test.startTest() and Test.stopTest(), it schedules MySchedulable to run. Salesforce executes the scheduled job synchronously at stopTest(), allowing the Account update to happen. However, the batch job enqueued inside the schedulable is not executed in the test context. Therefore, when checking Contacts, the assertion fails since their updates never occur during the unit test.
Here, the second assertion will fail because Salesforce does not execute nested asynchronous jobs (like the batch job) within Test.stopTest(). This means there is no direct way to test multi-layer asynchronous logic in one test. The recommended approach is to decompose tests. You should create separate unit tests for each layer: one for the schedulable logic and another for the batch logic. This ensures each piece is independently tested without relying on nested asynchronous execution.
Another important consideration for batch jobs is that Salesforce allows only one batch execution per unit test. If your test inadvertently runs multiple batches, it may throw exceptions. To avoid this, limit your test data or use techniques such as dependency injection. For example, expose your query in a @TestVisible variable so that unit tests can control it, ensuring that only one batch executes.
In summary, testing asynchronous Apex requires careful structuring of unit tests. You must use Test.startTest() and Test.stopTest() to execute asynchronous processes synchronously. For multi-layer asynchronous logic, decompose tests so each layer can be verified independently. For batch Apex, limit test data and use dependency injection where possible to avoid unexpected behavior during testing.
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