```swift
func testConcurrentAsyncOperation() {
    let exp = expectation(description: "\(#function)\(#line)")

    // Create the main operation
    let main = ConcurrentAsyncOperation()
    // The main completion block is executed after the operation has completed.
    main.completionBlock = {
        // Check if the data is received from the dependent operation
        print("The completion block is called.")
        main.completionBlock = nil
        exp.fulfill()
    }

    main.start()

    waitForExpectations(timeout: 40, handler: nil)
}
```