isTransportTestable_() {
    let testable = false;

    /** @suppress {visibility} suppression added to enable type checking */
    const transportType = this.channel_.determineTransportType_();
    switch (transportType) {
      case TransportTypes.NATIVE_MESSAGING:
        testable = true;
        break;
    }

    return testable;
  }
Determines if the transport type for the channel is testable.
Some transports are misusing global state or making other
assumptions that cause connections to fail.
@return {boolean} Whether the transport is testable.
@private