What are mocking and stubbing techniques for Combine in Swift?

        import Combine
        import XCTest

        class ExampleTests: XCTestCase {
            var cancellables: Set = []

            func testPublisherReturnsMockData() {
                // Mocking a publisher 
                let mockPublisher = Just("Mock Data")
                    .setFailureType(to: Error.self)
                    .eraseToAnyPublisher()

                // Subscribing to the mock publisher
                mockPublisher
                    .sink(receiveCompletion: { completion in
                        // Handle completion
                    }, receiveValue: { value in
                        // Asserting the value received is as expected
                        XCTAssertEqual(value, "Mock Data")
                    })
                    .store(in: &cancellables)
            }
            
            func testPublisherWithStubbing() {
                // Creating a stub for a network request
                let stubbedResponse = Just("Stubbed Response")
                    .setFailureType(to: Error.self)
                    .eraseToAnyPublisher()

                // Simulating a function that returns a publisher
                func fetchData() -> AnyPublisher {
                    return stubbedResponse
                }

                // Subscribing to the stubbed function
                fetchData()
                    .sink(receiveCompletion: { completion in
                        // Handle completion
                    }, receiveValue: { value in
                        // Asserting the value returned by the stubbed function is correct
                        XCTAssertEqual(value, "Stubbed Response")
                    })
                    .store(in: &cancellables)
            }
        }