RN 中最基本的 component 例如 View 和 TextInput 都有一个 prop 叫 testID -> 这里是官网说明。
可以用来做 end-to-end test 的 locator。那么它应该显示在哪里呢？根据 facebook 的 code，看起来应该是作为 content description 出现：

ReactTestHelper.java

/**
 * Gets the view with a given react test ID in the UI hierarchy. React test ID is currently
 * propagated into view content description.
 */
public static View getViewWithReactTestId(View rootView, String testId) {
  return findChild(rootView, hasTagValue(testId));
}

于是在 demo 中某个 render 加了类似如下 testID:

render: function() {
    return (
        <View style = {styles.container}>
        ...
        <View style = {styles.input}>
        <TextInput
        ...
        placeholder = {'Your Account'}
        testID = 'debug-signin-username-input' />
        </View>
        <View style = {styles.input}>
        <TextInput
        ...
        placeholder = {'Your Password'}
        testID = 'debug-signin-passwd-input' />
        </View>
        ...
        </View>
    );
},

build 好后用 uiautomator 一看，content-desc 是空的：

网上搜了搜发现这个帖子，原文-> React Native put testID into the tag of view, and accessibilityLabel into content description。accessibilityLabel 这个 prop 目前 View 才有，于是改成以下：

render: function() {
    return (
        <View style = {styles.container}>
        ...
        <View 
        style = {styles.input}
        accessibilityLabel = 'username-input'>
        <TextInput
        ...
        placeholder = {'Your Account'} />
        </View>
        <View 
        style = {styles.input}
        accessibilityLabel = 'passwd-input'>
        <TextInput
        ...
        placeholder = {'Your Password'} />
        </View>
        <TouchableNativeFeedback>            
        <View style={styles.submit}
        accessibilityLabel = 'signin-submit'>
        <Text style={styles.submitText}>
        SIGN IN
        </Text>
        </View>
        </TouchableNativeFeedback>
        </View>
    );
},

再用 uiautomator 看，content-desc 有了：

测试代码如下：

def test_find_elements(self):
    sleep(5)
    user_input = self.driver.find_element_by_accessibility_id("username-input")
    user_input.click()
    user_input.send_keys('test_account')
    pwd_input = self.driver.find_element_by_accessibility_id("passwd-input")
    pwd_input.click()
    pwd_input.send_keys('123456')
    signin_submit = self.driver.find_element_by_accessibility_id("signin-submit")
    signin_submit.click()

启动 Appium 跑测试代码，通过。