XCTAssertThrowsError for async/await function

Question

Given the following method signature, how can I test this method:

func doTheJob(param: String) async throws -> String

with XCTAssertThrowsError?

I've tried XCTAssertThrowsError(await object.doTheJob(param: "")) but getting an error:

'async' call in an autoclosure that does not support concurrency

What would be a solution to this problem?

Answer 1

It would be a good idea to submit a feature request for this using Feedback Assistant but for now you can create a func that XCTFail if the expression does not throw

func xCTAssertThrowsError<T>(_ expression: @autoclosure () async throws -> T) async {
    do {
        _ = try await expression()
        XCTFail("No error was thrown.")
    } catch {
        //Pass
    }
}

Then you can use it something like.

func testExample() async throws {

    await xCTAssertThrowsError(try await doSomething())
}

If you want to use the errorHandler and other arguments you can implement those too in your custom func.

func xCTAssertThrowsError<T>(
    _ expression: @autoclosure () async throws -> T,
    _ message: @autoclosure () -> String = "",
    file: StaticString = #filePath,
    line: UInt = #line,
    _ errorHandler: (Error) -> Void = { _ in }
) async {
    do {
        _ = try await expression()
        XCTFail(message())
    } catch {
        errorHandler(error)
    }
}