1// Avoid this pattern in tests
2let semaphore = DispatchSemaphore(value: 0)
3URLSession.shared.dataTask(with: url) { _, _, _ in
4    semaphore.signal()
5}.resume()
6semaphore.wait() // Risky on main test thread

1import XCTest
2
3final class APITests: XCTestCase {
4    func testFetchUser() {
5        let expectation = expectation(description: "Fetch user response")
6        let url = URL(string: "https://httpbin.org/json")!
7
8        URLSession.shared.dataTask(with: url) { data, response, error in
9            XCTAssertNil(error)
10            XCTAssertNotNil(data)
11            XCTAssertNotNil(response)
12            expectation.fulfill()
13        }.resume()
14
15        waitForExpectations(timeout: 5)
16    }
17}

1import XCTest
2
3final class AsyncAPITests: XCTestCase {
4    func testFetchStatusCode() async throws {
5        let url = URL(string: "https://httpbin.org/status/200")!
6        let (_, response) = try await URLSession.shared.data(from: url)
7
8        guard let http = response as? HTTPURLResponse else {
9            XCTFail("Expected HTTP response")
10            return
11        }
12
13        XCTAssertEqual(http.statusCode, 200)
14    }
15}

1import Foundation
2
3final class MockURLProtocol: URLProtocol {
4    static var responseData: Data?
5    static var response: URLResponse?
6    static var responseError: Error?
7
8    override class func canInit(with request: URLRequest) -> Bool { true }
9    override class func canonicalRequest(for request: URLRequest) -> URLRequest { request }
10
11    override func startLoading() {
12        if let response = Self.response {
13            client?.urlProtocol(self, didReceive: response, cacheStoragePolicy: .notAllowed)
14        }
15        if let data = Self.responseData {
16            client?.urlProtocol(self, didLoad: data)
17        }
18        if let error = Self.responseError {
19            client?.urlProtocol(self, didFailWithError: error)
20        } else {
21            client?.urlProtocolDidFinishLoading(self)
22        }
23    }
24
25    override func stopLoading() {}
26}

1import XCTest
2
3final class DelegateAPITests: XCTestCase, URLSessionDataDelegate {
4    var didReceiveData = false
5
6    func testDelegateCallback() {
7        let exp = expectation(description: "delegate callback")
8        let config = URLSessionConfiguration.ephemeral
9        let session = URLSession(configuration: config, delegate: self, delegateQueue: nil)
10        let url = URL(string: "https://httpbin.org/bytes/8")!
11
12        session.dataTask(with: url) { _, _, error in
13            XCTAssertNil(error)
14            exp.fulfill()
15        }.resume()
16
17        waitForExpectations(timeout: 5)
18        XCTAssertTrue(didReceiveData)
19    }
20
21    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
22        didReceiveData = true
23    }
24}