What method can be used to simulate callouts in test methods?

The method to simulate callouts in test methods is by using Test.setMock(). This method allows developers to define the behavior of HTTP callouts, which is particularly useful when writing unit tests for Salesforce applications that rely on external services.

By specifying a mock response using Test.setMock(), you can control the data returned from a web service call while the test executes. This is crucial because actual callouts to external services can introduce variability and latency in tests, making them unreliable. The mock responses ensure that tests run quickly and consistently, regardless of the state or availability of the external service.

When a test method calls an HTTP service, instead of performing the real call, it invokes the mock that was set with Test.setMock(). This approach leads to a more effective and stable testing environment where developers can validate their logic without reliance on external systems.