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@h-taro(Taro H)

SwiftでAPIクライアントのユニットテストを記述する

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概要

APIクライアントのテストを書きます。
APIにはQiitaのAPIを使用します。
環境にはPlaygroundを使用しました。

環境

Xcode 13.1

手順

  1. APIクライアントを準備する
  2. テスト書く

APIクライアントを準備する

今回の記事の目的から逸れるため、詳しくは解説しません。
コードは以下です。

Playground
import Foundation

enum SessionError: Error {
    case noData
    case noResponse
    case unAcceptableStatusCode(Int)
}

enum HttpMethod: String {
    case `get` = "GET"
    case post = "POST"
}

enum Result<T> {
    case success(T)
    case failure(Error)
}

protocol Requestable {
    associatedtype Response: Decodable
    var baseURL: URL { get }
    var path: String { get }
    var httpMethod: HttpMethod { get }
}

final class Session {
    func send<T: Requestable>(_ request: T, completion: @escaping (Result<T.Response>) -> ()) {
        let url = request.baseURL.appendingPathComponent(request.path)
        var urlRequest = URLRequest(url: url)
        urlRequest.httpMethod = request.httpMethod.rawValue
        
        let task = URLSession.shared.dataTask(with: urlRequest) { data, response, error in
            if let error = error {
                completion(.failure(error))
                return
            }
            
            guard let response = response as? HTTPURLResponse else {
                completion(.failure(SessionError.noResponse))
                return
            }
            
            guard 200..<300 ~= response.statusCode else {
                completion(.failure(SessionError.unAcceptableStatusCode(response.statusCode)))
                return
            }
            
            guard let data = data else {
                completion(.failure(SessionError.noData))
                return
            }
            
            do {
                let objects = try JSONDecoder().decode(T.Response.self, from: data)
                completion(.success(objects))
            } catch {
                completion(.failure(error))
            }
        }
        
        task.resume()
    }
}

struct Article: Codable {
    let title: String
}

struct ArticlesRequest: Requestable {
    typealias Response = [Article]
    var baseURL: URL = URL(string: "https://qiita.com")!
    var path: String = "/api/v2/items"
    var httpMethod: HttpMethod = .get
}

let session = Session()
let request = ArticlesRequest()

session.send(request) { result in
    switch result {
    case .success(let articles):
        print("[debug] \(articles.count)") // => [debug] 20
    case .failure(let error):
        print("[debug] \(error.localizedDescription)")
    }
}

ユニットテストを記述する

コードは以下です。

Playground
import XCTest
...
final class PlaygroundTests: XCTestCase {
    func testGetArticles() {
        let session = Session()
        let request = ArticlesRequest()
        let expectation = expectation(description: "")
        
        session.send(request) { result in
            switch result {
            case .success(let articles):
                XCTAssertNotNil(articles.first)
                expectation.fulfill()
            case .failure(let error):
                print(error)
            }
        }
        
        wait(for: [expectation], timeout: 5)
    }
}
PlaygroundTests.defaultTestSuite.run()

出力は以下のようになると思います。

Test Case '-[__lldb_expr_13.PlaygroundTests testGetArticles]' started.
Test Case '-[__lldb_expr_13.PlaygroundTests testGetArticles]' passed (1.482 seconds).
Test Suite 'PlaygroundTests' passed at 2021-12-07 07:03:11.673.
	 Executed 1 test, with 0 failures (0 unexpected) in 1.482 (1.485) seconds

非同期テストの注意点

非同期処理のテストを書くときに注目すべきは expectation です。
expectationを使わずにテストを書いた場合、処理が完了する前にテストコードが終わってしまいます。
そのため、失敗して欲しいテストが成功してしまいます。

もう一度、テストコードを確認しましょう。

コードの最初にexpectationを生成しています。
testGetArticles()の最後でexpectationが完了するまでwaitしています。(timeoutを5秒に設定しています。)

XCTAssertNotNil(articles.first)でレスポンスが取得できたことを確認できてから、
expectationをfulfillします。
これでexpectationが完了したことを通知します。

Playground
final class PlaygroundTests: XCTestCase {
    func testGetArticles() {
        let session = Session()
        let request = ArticlesRequest()
        let expectation = expectation(description: "")
        
        session.send(request) { result in
            switch result {
            case .success(let articles):
                XCTAssertNotNil(articles.first)
                expectation.fulfill()
            case .failure(let error):
                print(error)
            }
        }
        
        wait(for: [expectation], timeout: 5)
    }
}
PlaygroundTests.defaultTestSuite.run()

全体のコードです。

Playground
import Foundation
import XCTest

enum SessionError: Error {
    case noData
    case noResponse
    case unAcceptableStatusCode(Int)
}

enum HttpMethod: String {
    case `get` = "GET"
    case post = "POST"
}

enum Result<T> {
    case success(T)
    case failure(Error)
}

protocol Requestable {
    associatedtype Response: Decodable
    var baseURL: URL { get }
    var path: String { get }
    var httpMethod: HttpMethod { get }
}

final class Session {
    func send<T: Requestable>(_ request: T, completion: @escaping (Result<T.Response>) -> ()) {
        let url = request.baseURL.appendingPathComponent(request.path)
        var urlRequest = URLRequest(url: url)
        urlRequest.httpMethod = request.httpMethod.rawValue
        
        let task = URLSession.shared.dataTask(with: urlRequest) { data, response, error in
            if let error = error {
                completion(.failure(error))
                return
            }
            
            guard let response = response as? HTTPURLResponse else {
                completion(.failure(SessionError.noResponse))
                return
            }
            
            guard 200..<300 ~= response.statusCode else {
                completion(.failure(SessionError.unAcceptableStatusCode(response.statusCode)))
                return
            }
            
            guard let data = data else {
                completion(.failure(SessionError.noData))
                return
            }
            
            do {
                let objects = try JSONDecoder().decode(T.Response.self, from: data)
                completion(.success(objects))
            } catch {
                completion(.failure(error))
            }
        }
        
        task.resume()
    }
}

struct Article: Codable {
    let title: String
}

struct ArticlesRequest: Requestable {
    typealias Response = [Article]
    var baseURL: URL = URL(string: "https://qiita.com")!
    var path: String = "/api/v2/items"
    var httpMethod: HttpMethod = .get
}

final class PlaygroundTests: XCTestCase {
    func testGetArticles() {
        let session = Session()
        let request = ArticlesRequest()
        let expectation = expectation(description: "")
        
        session.send(request) { result in
            switch result {
            case .success(let articles):
                XCTAssertNotNil(articles.first)
                expectation.fulfill()
            case .failure(let error):
                print(error)
            }
        }
        
        wait(for: [expectation], timeout: 5)
    }
}
PlaygroundTests.defaultTestSuite.run()

参考リンク

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