The nfc-helpers.js requires an implementation of the WebNFCTest interfaces, which should emulate platform Web NFC backends.

The WebNFCTest interface is defined as:

 class NFCTestChromium { initialize(); // Sets up the testing environment. async reset(); // Frees the resources. getMockNFC(); // Returns `MockNFC` interface. }; class MockNFC { setHWStatus(number status); // Sets the hardware status. setReadingMessage(NDEFMessageInit message); // Sets message that is used to deliver NFC reading updates. setPendingPushCompleted(boolean result); // Sets if the pending push is completed. setPushShouldTimeout(boolean result); // Sets flag to trigger the pending push to timeout. pushedMessage(); // Gets the pushed `NDEFMessageSource`. pushOptions(); // Gets the pushed `NDEFPushOptions`. setIsNDEFTech(boolean isNDEF); // Sets if the NFC device exposes NDEF technology. setIsFormattedTag(boolean isFormatted); // Sets if the NFC tag has formatted NDEF message. }; 

The Chromium implementation of the WebNFCTest interface is located in nfc-mock.js.

Other browser vendors should provide their own implementations of the WebNFCTest interfaces.