Fix flaky test, BatteryStatsHistoryIteratorTest

import static com.google.common.truth.Truth.assertThat;

import android.content.Context;

import android.os.BatteryManager;

import android.os.BatteryStats;

import android.os.Process;

import androidx.test.InstrumentationRegistry;

import androidx.test.filters.SmallTest;

import androidx.test.runner.AndroidJUnit4;

import libcore.testing.io.TestIoUtils;

import org.junit.Before;

import org.junit.Test;

import org.junit.runner.RunWith;

    @Before

    public void setup() {

        Context context = InstrumentationRegistry.getContext();

        File historyDir = new File(context.getDataDir(), BatteryStatsHistory.HISTORY_DIR);

        String[] files = historyDir.list();

        if (files != null) {

            for (int i = 0; i < files.length; i++) {

                new File(historyDir, files[i]).delete();

            }

        }

        historyDir.delete();

        final File historyDir =

                TestIoUtils.createTemporaryDirectory(getClass().getSimpleName());

        mBatteryStats = new MockBatteryStatsImpl(mMockClock, historyDir);

    }