Ios swift – XCTestCase Multipart params with Alamofire using URLProtocolStub in Swift

I would like to know how can I test multipart sending params with Alamofire (network stack). Ex: send a string with an image (Data type).

My issue is that when I receive a response, I get the URLRequest and I check the httpBody for getting my params. Unfortunately it is nil and I don’t know another way to get multipartData.

(I’ve already do some search before asking here ;))

For Doing this, I create a stub URLProtocol (called URLProtocolStub)

final class URLProtocolStub: URLProtocol {
    private struct Stub {
        let data: Data?
        let response: URLResponse?
        let error: Error?
        let requestObserver: ((URLRequest) -> Void)?
    }
    
    private static var _stub: Stub?
    private static var stub: Stub? {
        get { return queue.sync { _stub } }
        set { queue.sync { _stub = newValue } }
    }
    
    private static let queue = DispatchQueue(label: "URLProtocolStub.queue")
    
    static func stub(data: Data?, response: URLResponse?, error: Error?) {
        stub = Stub(data: data, response: response, error: error, requestObserver: nil)
    }
    
    static func observeRequests(observer: @escaping (URLRequest) -> Void) {
        stub = Stub(data: nil, response: nil, error: nil, requestObserver: observer)
    }
    
    override class func canInit(with request: URLRequest) -> Bool {
        return true
    }
    
    override class func canonicalRequest(for request: URLRequest) -> URLRequest {
        return request
    }
    
    override func startLoading() {
        guard let stub = URLProtocolStub.stub else { return }
        
        if let data = stub.data {
            client?.urlProtocol(self, didLoad: data)
        }
        
        if let response = stub.response {
            client?.urlProtocol(self, didReceive: response, cacheStoragePolicy: .notAllowed)
        }
        
        if let error = stub.error {
            client?.urlProtocol(self, didFailWithError: error)
        } else {
            client?.urlProtocolDidFinishLoading(self)
        }
        
        stub.requestObserver?(request)
    }
}

And I set it on the URLConfigurationSession for use a fake session on Alamaofire.

let configuration = URLSessionConfiguration.af.ephemeral
configuration.protocolClasses = [URLProtocolStub.self] 

Finally, my test function for testing HTTP request with multipart data.

func test_uploadMultipart_with_params() async {
        // 1
        let httpURL = HTTPURLResponse(statusCode: 204)
        let bodyParams = ["firstname": "mock", "lastname": "test"]
        let imageData = UIColor.yellow.image(CGSize(width: 128, height: 128)).jpegData(compressionQuality: 0.7)

        URLProtocolStub.stub(data: nil, response: httpURL, error: nil)

        let exp = expectation(description: "Waiting to receive response")

        // 2
        let loggerDelegate = StubHTTPLoggerDelegate(didReceivedResponse: { request in
            XCTAssertEqual(request?.httpBody.flatMap { String(data: $0, encoding: .utf8) }, "firstname=mock&lastname=test")
            exp.fulfill()
        })

        // 3
        let result = await makeSUT(loggerDelegate: loggerDelegate).requestMultipart(imageDatas: [imageData], pathType: anyPathType(.post, bodyParameters: bodyParams, urlParameters: nil))

        do { try result.get() } catch { XCTFail("(error)") }

        wait(for: [exp], timeout: 1.0)
    }

I explain this function step by step :

1. I prepare my bodyParams & image for my multipart request.
2. I create a listener for listen HTTP response when received.
3. And I create my AlamofireHTTPClient (makeSUT function) by passing my listener and call my Alamorefire requestMultipart with my bodyParams & image. Then a execute my client.

My test is checking if I am sending the right parameters on a Alamofire multipart request.
This test failed because the httpBody from a request (URLRequest) is nil and I don’t know how to get my multipart params to test it :(.

Thanks for helping me :).