The Apex test fails in the Test Runner but succeeds in the Execute Anonymous window because the test method relies on existing data in the sandbox.
Isolation of Test Data: By default, Apex tests do not have access to pre-existing data in the organization. Tests are executed in an isolated context to ensure they are not dependent on external data, promoting reliability and repeatability.
"Apex test methods don’t have access to pre-existing data in the organization. The test methods have access to all data that they create and to changes made by other test methods (unless the @IsTest(Isolated=true) annotation is used)."— Apex Developer Guide: Isolation of Test Data from Organization Data in Unit Tests
Execute Anonymous Window: When code is run in the Execute Anonymous window, it executes in the current user's context and has access to all organization data, including existing records.
"All Apex code runs in system mode. The only exception is anonymous blocks, such as code executed using the Execute Anonymous window or the SOAP API."— Apex Developer Guide: Enforcing Object and Field Permissions
Solution: To fix the failing test, the developer should create the necessary test data within the test method or use the @IsTest(SeeAllData=true) annotation if access to existing data is absolutely necessary (though this is generally discouraged).
"If you specify @IsTest(SeeAllData=true), the test method has access to all data in the organization, but the test can be slower and less reliable because it might depend on data that changes."— Apex Developer Guide: Using the SeeAllData Annotation
Why Other Options Are Incorrect:
Option A: While calling an @future method requires special handling in tests, it would not cause the method to pass in Execute Anonymous and fail in tests.
Option C: A syntax error would prevent the code from compiling, so it wouldn't run in either context.
Option D: Using System.runAs is only necessary when testing code that behaves differently for users with different profiles or permissions.
Conclusion: The discrepancy arises because the test method is attempting to access data that isn't available in the test context, leading to its failure in the Test Runner but success in the Execute Anonymous window.
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