I've read the Kotlin append to file thread, and my UIAutomator code looks like:

fun appendLog(text: String?) {
    val logFile = File("/sdcard/Download/autotest.log")
    if (!logFile.exists()) {
        try {
            logFile.createNewFile()
            Log.d(TAG, "Create new file $logFile Succeed!")
        } catch (e: IOException) {
            Log.e(TAG, "Create new file $logFile FAILED!, $e")
        }
    }
    try {
        FileOutputStream(logFile, true).bufferedWriter().use { writer ->
            writer.append(text)
            writer.newLine()
        }
    } catch (e: IOException) {
        Log.e(TAG, "Appending file $logFile FAILED!, $e")
    }
}

// test cas 1
appendLog("Some test result")

// test cas 2
appendLog("Other test results")

But got error from adb logcat

03-14 20:16:57.829 27499 27522 D LogTest : Create new file /sdcard/Download/autotest.log Succeed!
03-14 20:16:57.830 27499 27522 E LogTest : Appending file /sdcard/Download/autotest.log FAILED!, java.io.FileNotFoundException: /sdcard/Download/autotest.log: open failed: EEXIST (File exists)

03-14 20:17:02.214 27499 27522 D LogTest : Create new file /sdcard/Download/autotest.log Succeed!
03-14 20:17:02.216 27499 27522 E LogTest : Appending file /sdcard/Download/autotest.log FAILED!, java.io.FileNotFoundException: /sdcard/Download/autotest.log: open failed: EEXIST (File exists)