Apex Test coverage on External Objects

Question

How can the Test Coverage can be fulfilled for the Apex classes which queried for External Objects.I have written Test class just like assuming External Object behaves like a custom Object but getting error repetitively "CANNOT_INSERT_UPDATE_ACTIVATE_ENTITY: You can't create records for the object".

I used the DML statements like Database.insertAsync but no use. Gone through some articles saying that we need to mock the external object for the Apex Test coverage on External Object. If so is there document which explains about this concept.

Answer 1

Typically we just set up a simple mock for this type of testing. You can have a class which just passes records through normally, but then when you overwrite it passes whatever you choose:

public virtual inherited sharing class Query
{
    public static List<SObject> records(List<SObject> records)
    {
        return instance.passThrough(records);
    }

    static Query instance = new Query();
    @TestVisible static void setMock(Query mock) { instance = mock; }

    protected virtual List<SObject> passThrough(List<SObject> records)
    {
        return records;
    }
}

Once you've got this mocking set up, wrap your query in this method in your service:

public with sharing class MyService
{
    public static void doStuff()
    {
        for (My_External_Object__x record : Query.records([
            SELECT ... FROM My_External_Object__x
        ])){
            // logic
        }
    }
}

In your test, usage would then look like:

@IsTest
class MyTests
{
    class Mock extends Query
    {
        final List<My_External_Object__x> externalRecords;
        Mock(List<My_External_Object__x> externalRecords)
        {
            this.externalRecords = externalRecords;
        }

        protected override List<SObject> passThrough(List<SObject> records)
        {
            return externalRecords;
        }
    }

    @IsTest staticVoid testStuff()
    {
        List<My_External_Object__x> mockRecords = new List<My_External_Object__x>();
        // populate as desired

        Query.setMock(new Mock(mockRecords));

        Test.startTest();
            MyService.doStuff();
        Test.stopTest();

        // make assertions
    }
}