How do I set up unit tests and mocks with URLSession in Swift?

Unit testing in Swift can be quite straightforward, especially when working with URLSession. To effectively test code that relies on network requests, you'll want to create a mock URLSession. This allows you to simulate network responses without making actual HTTP requests. Below, you will find an example of how to set up unit tests and mocks with URLSession in Swift.


        import XCTest
        import Foundation

        // Define a protocol for URLSession to allow mocking
        protocol URLSessionProtocol {
            func dataTask(with url: URL, completionHandler: @escaping (Data?, URLResponse?, Error?) -> Void) -> URLSessionDataTask
        }

        extension URLSession: URLSessionProtocol {
            func dataTask(with url: URL, completionHandler: @escaping (Data?, URLResponse?, Error?) -> Void) -> URLSessionDataTask {
                return dataTask(with: url, completionHandler: completionHandler)
            }
        }

        // Create a mock URLSession for testing
        class MockURLSession: URLSessionProtocol {
            var mockedData: Data?
            var mockedError: Error?

            func dataTask(with url: URL, completionHandler: @escaping (Data?, URLResponse?, Error?) -> Void) -> URLSessionDataTask {
                completionHandler(mockedData, nil, mockedError)
                return URLSessionDataTask() // Return a dummy task
            }
        }

        // Example network manager using URLSession
        class NetworkManager {
            var session: URLSessionProtocol

            init(session: URLSessionProtocol = URLSession.shared) {
                self.session = session
            }

            func fetchData(from url: URL, completion: @escaping (Data?, Error?) -> Void) {
                session.dataTask(with: url) { data, response, error in
                    completion(data, error)
                }.resume()
            }
        }

        // Unit tests
        class NetworkManagerTests: XCTestCase {
            var networkManager: NetworkManager!
            var mockSession: MockURLSession!

            override func setUp() {
                super.setUp()
                mockSession = MockURLSession()
                networkManager = NetworkManager(session: mockSession)
            }

            func testFetchData_Success() {
                let expectedData = "Test data".data(using: .utf8)
                mockSession.mockedData = expectedData

                let expectation = self.expectation(description: "Completion Handler Called")

                networkManager.fetchData(from: URL(string: "http://test.com")!) { data, error in
                    XCTAssertNil(error)
                    XCTAssertEqual(data, expectedData)
                    expectation.fulfill()
                }

                waitForExpectations(timeout: 1, handler: nil)
            }

            func testFetchData_Error() {
                let expectedError = NSError(domain: "", code: 1, userInfo: nil)
                mockSession.mockedError = expectedError

                let expectation = self.expectation(description: "Completion Handler Called")

                networkManager.fetchData(from: URL(string: "http://test.com")!) { data, error in
                    XCTAssertNotNil(error)
                    XCTAssertEqual((error as NSError?)?.code, 1)
                    expectation.fulfill()
                }

                waitForExpectations(timeout: 1, handler: nil)
            }
        }

Unit Testing Swift URLSession Mocking XCTest Networking Functional Testing

How do I set up unit tests and mocks with URLSession in Swift?

Popular Topics

Recent Languages

How do I set up unit tests and mocks with URLSession in Swift?

Related Questions

Popular Topics

Recent Languages