Which functionality does the system method "runAs()" verify when writing test methods?

Purpose of runAs():

The runAs() system method is used in test methods to verify record sharing and access based on user roles, profiles, and sharing rules.

It does not enforce Field-Level Security (FLS) or object permissions, which need to be explicitly tested in the code.

Why Option A is Correct:

runAs() ensures that the sharing rules of the specified user are applied during the test, validating sharing-based access controls.

Why Others Are Incorrect:

Option B: FLS is not enforced by runAs().

Option C: Permissions are not enforced by runAs(); only record-level sharing is validated.

For more information, see Salesforce documentation on runAs(): https://help.salesforce.com/