Is there a way through which we can add a testID and accessibilityLabel to header buttons like the header back button in order to be able to write automated tests?

Depending on how you are setting the buttons in your header will depend on how you set a testID, etc.

Back button

For the <Back button. It uses the component HeaderBackButton.jsx it comes with the accessibilityLabel, the accessibilityRole set, which you can see here.

accessibilityRole="button"
accessibilityLabel={accessibilityLabel}
testID={testID}

In the signature of the function that creates the back button you can set the accessibilityLabel and the testID which you can see here. This is the default value of the accessibilityLabel:

accessibilityLabel = label && label !== 'Back' ? `${label}, back` : 'Go back',

React-Native Button

If you are using the <Button /> component from react-native you can just pass the testID and accessibilityLabel that you want.

static navigationOptions = {
  headerTitle: 'Title',
  headerRight: (
    <Button
      onPress={() => alert('This is a button!')}
      title="Right"
      color="#000"
      testID='headerRightButton'
      accessibilityLabel="Right button!"
    />
  ),
  headerLeft: (
    <Button
      onPress={() => alert('This is a button!')}
      title="Left"
      color="#000"
      testID='headerLeftButton'
      accessibilityLabel="Left button!"
    />
  )
};

#Your own buttons If you have created your own buttons to use then you will have to handle these yourself and pass the props down to the Touchable part of your component, see the documentation for more information https://facebook.github.io/react-native/docs/accessibility#accessibilitylabel-ios-android

Here's a basic example of what you could do

class MyButton extends Component {
  render() {
    return (
      <TouchableOpacity onPress={() => {}}
       testID={this.props.testID}
       accessibilityLabel={this.props.accessibilityLabel}
      >
        <View>  
         // style your awesome button here
        </View>
      </TouchableOpacity>
    );
  }
}

Which you could then call like

<MyButton
 testID={'mybutton'}
 accessibilityLabel={'tap my button'} />

You could/should probably set prop defaults on the testID etc