XCTestCase extension with boilerplate code for unit testing async functions (waiting for expectations)

XCTestCase+Expectation.swift

//
//  AsyncTests.swift
//

import XCTest

// MARK: Async Helper Extension

extension XCTestCase {
	
	/// Helper function for setting up a single expectation; call expectation.fulfill() to complete expectation.
	func wait(description: String = "\(NSURL(fileURLWithPath: #file).lastPathComponent ?? #file) \(#function)", timeout: TimeInterval = 0.5, testingClosure: (_ expectation: XCTestExpectation) -> Void) {
		let expectation = expectationWithDescription(description)
		testingClosure(expectation)
		waitForExpectationsWithTimeout(timeout, handler: nil)
	}
}

// MARK: Example & Usage

class AsyncTests: XCTestCase {
	
	func testExample() {
		
		// Wrap the the async call using the helper function.
		wait { expectation in
			
			// Call your async function that you want to unit test.
			asyncFunction { result in
				
				XCTAssertEqual(result, "Success")
				
				// Complete expectation
				expectation.fulfill()
			}
		}
	}
}

/// Async Function to unit test.
private func asyncFunction(completion: String -> Void) {
	dispatch_async(dispatch_get_main_queue()) {
		completion("Success")
	}
}

Updated to Swift 3