Recording a Unit-Test Coverage of a particular async function

Goal: To Unit Test the following:

    @objc func handleSendButton() {
        guard let profileData: VLProfile = VLRunTime.shared.profile else { return }
        let memberInfo = VLMemberInfo(firstName: profileData.profile?.firstName ?? "", lastName: profileData.profile?.lastName ?? "", memberId: profileData.profile?.cisNumber ?? "", phone: profileData.profile?.primaryPhone ?? "")
        vlSpinner?.isHidden = false
        stackView?.isUserInteractionEnabled = false
        var requestID: String = ""
        if !didSendMessage {
            requestID = self.requestID ?? ""
        }
        VLConciergeManager.sendSecureMessage(message: textView?.text ?? "",
                                             subject: subjectLabelTextField?.text ?? "",
                                             requestID: requestID,
                                             member: memberInfo) { response, error in
            callInMain {
                self.stackView?.isUserInteractionEnabled = true
                self.vlSpinner?.isHidden = true
                if (response?.status) != nil {
                    // naviagte to the success screen
                    if self.didSendMessage {
                        let successViewController = VLConciergeConfirmSecuredMessageViewController.load(from: .concierge)
                        self.navigationController?.pushViewController(successViewController, animated: true)
                    } else {
                        self.navigationController?.popViewController(animated: true)
                    }
                } else {
                    showToast((error?.description ?? "Error"), type: .failure)
                }
            }
        }
    }
}

... so I get its Coverage Graph:

enter image description here

I can make an async unit test of the inclosed VLConciergeManager.sendSecureMessage() but it doesn't register in the respective function coverage. I need to test the whole handleSendButton().

The best that I can do is to populate the required parameters and call the instantiated handler function:

func testHandleSendButton() {
    VLRunTime.shared.profile = getProfile()
    let rootController = VLConciergeSendReplyViewController()
    let _ = UINavigationController(rootViewController: rootController)
    rootController.handleSendButton()
}

But I don't know how to determine the outcome from within the test(), being it is an async function and I can't mess around with the target code; although I need to determine if the outcome is successful or not (I'll accept that the callback was made), the test has to be passive; I can't touch the target code.

Question: how do I correctly do a unit test of 'handleSendButton()' so I get the respective coverage recorded?