sMock - Swift mocking framework for Unit-tests (thanks gMock for ideas)

Problem

Moving into the Swift world from ObjC / C ++, I ran into a problem when writing unit tests: the lack of tools for creating Mock objects.

When writing decomposed code, we often hide implementation details behind interfaces (protocols). It is also very convenient to check the functionality of an object separately from others, replacing its component parts with mokami.

Googling, I found several Swift Mocking frameworks on github. But none of them appeared to me clear and obvious in use (for one or several reasons):

• has a cloud of dependencies
• no intuitive syntax
• code generation / manual writing of a large amount of auxiliary code is required
• not integrated with XCTest (allows wet, but not tested)
• to have many features dumped into a bunch of one framework (confusion of what and why)
• should be used with a limited number of predefined / built-in types

This situation was unpleasant for me, and for about a year I used workarounds and self-made mokas.
Self-written mock objects are simple, but they

• different every time (reinvent the wheel)
• or the same each time (copy-paste)
• unobvious to use

Decision

C ++ gTest / gMock ( Google).
Mock- . , «» ( ) .

gMock, sMock (Swift Mock) gMock.
https://github.com/Alkenso/sMock

sMock:

• mock /
• expectations
• - mock-
• XCTest.framework
• zero-dependency
• pure Swift

()

sMock

• Mock , ( )
• Mock methodCall. "" .

Mocking synchronous method

:

import XCTest
import sMock

//    ,   
protocol HTTPClient {
    func sendRequestSync(_ request: String) -> String
}

//  Mock 
class MockHTTPClient: HTTPClient {
    //   call's mock entity.
    let sendRequestSyncCall = MockMethod<String, String>()

    func sendRequestSync(_ request: String) -> String {
        //  1.    Mock-
        //  2.  non-void   "default"    'Unexpected call' (..     ,   ).
        sendRequestSyncCall.call(request) ?? ""
    }
}

//  ,    
struct Client {
    let httpClient: HTTPClient

    //  ,  HTTP ,    .
    func retrieveRecordsSync() -> [String] {
        let response = httpClient.sendRequestSync("{ action: 'retrieve_records' }")
        return response.split(separator: ";").map(String.init)
    }
}

class ExampleTests: XCTestCase {
    func test_Example() {
        let mock = MockHTTPClient()
        let client = Client(httpClient: mock)

        //     expectation,    'sendRequestSync'  HTTPClient     'request'  "{ action: 'retrieve_records' }".
        //   ,      1     "r1;r2;r3".
        mock.sendRequestSyncCall
            //    expectation (      );
            .expect("Request sent.")
            //  ,   expectation    ,      match
            .match("{ action: 'retrieve_records' }")
            //    ,        (   match)
            .willOnce(
                //  ,    .
                .return("r1;r2;r3"))

        //   expectations,   Client-    .
        let records = client.retrieveRecordsSync()
        XCTAssertEqual(records, ["r1", "r2", "r3"])
    }
}

Mocking synchronous method + mocking asynchonous callback

Mock callback'a, .

//    ,   
protocol HTTPClient {
    func sendRequestSync(_ request: String) -> String
}

//  Mock 
class MockHTTPClient: HTTPClient {
    //   call's mock entity.
    let sendRequestSyncCall = MockMethod<String, String>()

    func sendRequestSync(_ request: String) -> String {
        //  1.    Mock-
        //  2.  non-void   "default"    'Unexpected call' (..     ,   ).
        sendRequestSyncCall.call(request) ?? ""
    }
}

//  ,    
struct Client {
    let httpClient: HTTPClient

    //  ,  HTTP ,    .   
    func retrieveRecordsAsync(completion: @escaping ([String]) -> Void) {
        let response = httpClient.sendRequestSync("{ action: 'retrieve_records' }")
        completion(response.split(separator: ";").map(String.init))
    }
}

class ExampleTests: XCTestCase {
    func test_Example() {
        let mock = MockHTTPClient()
        let client = Client(httpClient: mock)

        //     expectation,    'sendRequestSync'  HTTPClient     'request'  "{ action: 'retrieve_records' }".
        //   ,      1     "r1;r2;r3".
        mock.sendRequestSyncCall
            //    expectation (      );
            .expect("Request sent.")
            //  ,   expectation    ,      match
            .match("{ action: 'retrieve_records' }")
            //    ,        (   match)
            .willOnce(
                //  ,    .
                .return("r1;r2;r3"))

        //    expectation    ( ). 
        //     ,     -  :  'MockClosure' mock entity.
        //     expectation,      1    ( ) ["r1", "r2", "r3"].
        let completionCall = MockClosure<[String], Void>()
        completionCall
            //    expectation (      );
            .expect("Records retrieved.")
            //  ,   expectation    ,      match
            .match(["r1", "r2", "r3"])
            //    ,        (   match).
            //   return value   Void, .return   .
            .willOnce()

        //   expectations,   Client-.
        client.retrieveRecordsAsync(completion: completionCall.asClosure())

        //      expectations (  " "    ).
        sMock.waitForExpectations()
    }
}

Matchers, Actions, Argument capture

sMock (. ):

• Matchers — , .match: .any ( )
• Actions: expectation match'e .return, .
• : expectation .
• : , unexpectedCall

.
.
: , . .

, Swift .
, sMock . .
"testing with Swift"!

Try sMock on github (with SwiftPackageManager)