import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Stream;

public class Main {
    public static void main(String[] args) {
        final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        final BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
        try {
            int T = Integer.parseInt(br.readLine().trim());
            for (int i = 0; i < T; ++i) {
                IRunner runner = new Runner(br, bw);
                runner.run();
                runner.flush();
            }
            br.close();
            bw.close();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }
}

class Runner implements IRunner {
    final IReader reader;
    final BufferedWriter bw;
    final StringBuilder sb = new StringBuilder();

    final int nRows = 2, nCols;
    final int[][] values;
    final int[][] dp;

    Runner(BufferedReader br, BufferedWriter bw) {
        this.reader = new Reader(br);
        this.bw = bw;
        try {
            nCols = reader.readInts()[0];
            values = new int[nRows][];
            dp = new int[nRows][nCols];
            for (int i = 0; i < nRows; ++i) {
                values[i] = reader.readInts();
            }
            sb.ensureCapacity(20);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public void flush() {
        try {
            bw.write(sb.toString());
            bw.flush();
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
    }

    @Override
    public void run() throws IOException {
        for (int col = 0; col < nCols; ++col) {
            if (col == 0) {
                dp[0][col] = values[0][col];
                dp[1][col] = values[1][col];
            } else if (col == 1) {
                dp[0][col] = dp[1][col - 1] + values[0][col];
                dp[1][col] = dp[0][col - 1] + values[1][col];
            } else {
                {
                    // row 0
                    var case1 = dp[1][col - 1] + values[0][col];
                    var case2 = dp[1][col - 2] + values[0][col];
                    dp[0][col] = Math.max(case1, case2);
                }
                {
                    // row 1
                    var case1 = dp[0][col - 1] + values[1][col];
                    var case2 = dp[0][col - 2] + values[1][col];
                    dp[1][col] = Math.max(case1, case2);
                }
            }
        }
        var result = Math.max(dp[0][nCols - 1], dp[1][nCols - 1]);
        sb.append(result).append('\n');
    }
}

class Reader implements IReader {
    private BufferedReader br;

    public Reader(BufferedReader br) {
        this.br = br;
    }

    @Override
    public void skipLine() throws IOException {
        br.readLine();
    }

    @Override
    public Stream<String> lines() throws IOException {
        return br.lines();
    }

    @Override
    public String line() throws IOException {
        return br.readLine();
    }

    @Override
    public int[] readInts() throws IOException {
        String[] tokens = br.readLine().split(" ");
        int[] ints = new int[tokens.length];
        for (int i = 0; i < tokens.length; ++i) {
            ints[i] = Integer.parseInt(tokens[i]);
        }
        return ints;
    }

    @Override
    public List<Integer> readIntegers() throws IOException {
        String[] tokens = br.readLine().split(" ");
        var res = new ArrayList<Integer>(tokens.length);
        for (String token : tokens) {
            res.add(Integer.valueOf(token));
        }
        return res;
    }
}

interface IRunner {
    void run() throws IOException;

    void flush();
}

interface IReader {
    void skipLine() throws IOException;

    Stream<String> lines() throws IOException;

    String line() throws IOException;

    List<Integer> readIntegers() throws IOException;

    int[] readInts() throws IOException;
}