package contest230224;
import java.io.*;
import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.InputMismatchException;
import java.util.Queue;
import java.util.function.IntUnaryOperator;
import java.util.function.LongUnaryOperator;

public class H {
	InputStream is;
	FastWriter out;

	String INPUT = "";

	// できるだけ後ろのほうが良い？

	public void solve()
	{
		prepareFFT(1<<20);
		for(int T = ni();T > 0;T--)go();
	}

	void go()
	{
		int n = ni(), m = ni();
		char[] s = ns(n);
		char[] t = ns(m);
		int q = Integer.highestOneBit(s.length)<<2;
		prepareFFT(q);
		int[] plus = new int[n];
		for(int i = 0;i < 26;i+=2){
			double[] sre = new double[q];
			double[] sim = new double[q];
			for(int j = 0;j < n;j++){
				sre[j] = s[j] == 'a'+i || s[j] == '?' ? 1 : 0;
				sim[j] = s[j] == 'a'+i+1 || s[j] == '?'  ? 1 : 0;
			}

			double[] tre = new double[q];
			double[] tim = new double[q];
			for(int j = 0;j < m;j++){
				tre[j] = t[m-1-j] == 'a'+i || t[m-1-j] == '?' ? 1 : 0;
				tim[j] = t[m-1-j] == 'a'+i+1 || t[m-1-j] == '?' ? -1 : 0;
			}

			double[][] sr = doFFFT(sre, sim);
			double[][] tr = doFFFT(tre, tim);
			double[][] fced = new double[2][q];
			for(int j = 0;j < q;j++){
				fced[0][j] = (sr[0][j]*tr[0][j]-sr[1][j]*tr[1][j])/q;
				fced[1][j] = (sr[0][j]*tr[1][j]+sr[1][j]*tr[0][j])/-q;
			}
			double[][] rev = doFFFT(fced[0], fced[1]);
//			tr(rev[0]);
			for(int j = 0;j < n;j++){
				plus[j] += Math.round(rev[0][j+m-1]);
			}
		}
		for(int j = n-1;j >= 0;j--){
			if(plus[j] == m){
				for(int k = 0;k < n;k++){
					if(s[k] == '?'){
						s[k] = 'a';
					}
				}
				for(int k = 0;k < m;k++){
					s[j+k] = t[k];
				}
				out.println(s);
				return;
			}
		}
		out.println(-1);
	}
//
//	static double[] trans(double[] a)
//	{
//		double[] b = new double[a.length];
//		for(int i = 0;i < a.length;i++){
//			b[i] = a[rev[i]];
//		}
//		return b;
//	}

	public static double[][] doFFT(double[] srcRe, double[] srcIm)
	{
		int n = srcRe.length;
		if(Integer.bitCount(n) != 1)return null;
		int[] rev = reverseBitOrder(n);

		double[] dstRe = new double[n];
		double[] dstIm = new double[n];

		for(int i = 0;i < n;i++){
			dstRe[i] = srcRe[rev[i]];
			dstIm[i] = srcIm[rev[i]];
		}

		for(int s = 2;s <= n;s <<= 1){
			int nt = s >>> 1;
			int bs = nt;

			double wRe = 1.0;
			double wIm = 0.0;
			double uRe = Math.cos(Math.PI / bs);
			double uIm = -Math.sin(Math.PI / bs);

			for(int t = 0;t < nt;t++){
				for(int j = t; j < n;j += s){
					int jp = j + bs;
					double re = dstRe[jp]*wRe - dstIm[jp]*wIm;
					double im = dstRe[jp]*wIm + dstIm[jp]*wRe;
					dstRe[jp] = dstRe[j] - re;
					dstIm[jp] = dstIm[j] - im;
					dstRe[j] += re;
					dstIm[j] += im;
				}
				double nwRe = wRe*uRe - wIm*uIm;
				double nwIm = wRe*uIm + wIm*uRe;
				wRe = nwRe;
				wIm = nwIm;
			}
		}
		return new double[][]{dstRe, dstIm};
	}

	protected static int[] reverseBitOrder(int n)
	{
		int[] ret = new int[n];
		ret[0] = 0;
		for(int i = 1, h = n>>1;i < n;i <<= 1, h >>>= 1){
			for(int j = 0;j < i;j++){
				ret[j+i] = ret[j] + h;
			}
		}
		return ret;
	}

	public static int[] convolve(int[] a, int[] b)
	{
		int m = Integer.highestOneBit(a.length|b.length)<<2;
		prepareFFT(m);
		double[][] fa = doFFFT(a, m);
		double[][] fb = doFFFT(b, m);
		double[][] fced = new double[2][m];
		for(int i = 0;i < m;i++){
			fced[0][i] = (fa[0][i]*fb[0][i]-fa[1][i]*fb[1][i])/m;
			fced[1][i] = (fa[0][i]*fb[1][i]+fa[1][i]*fb[0][i])/-m;
		}
		double[][] ced = doFFFT(fced[0], fced[1]);
		int[] ret = new int[m];
		for(int i = 0;i < m;i++){
			ret[i] = (int)Math.round(ced[0][i]);
		}
		return ret;
	}

	static int[] rev;
	static double[] coss;
	public static void prepareFFT(int n)
	{
		rev = reverseBitOrder(n);
		coss = new double[n+1];
		for(int i = 0;i <= n>>>1;i++){
			coss[n-i] = coss[i] = Math.cos(Math.PI*i/(n>>>1));
		}
	}

	public static double[][] doFFFT(int[] srcRe, int n)
	{
		int m = srcRe.length;
		double[] dstRe = new double[n];
		double[] dstIm = new double[n];

		for(int i = 0;i < n;i++){
			if(rev[i] < m){
				dstRe[i] = srcRe[rev[i]];
			}
		}

		for(int s = 2;s <= n;s <<= 1){
			int nt = s >>> 1;
			int bs = nt;

			for(int t = 0;t < nt;t++){
				double wRe = coss[t*(n/s)];
				double wIm = coss[(n>>>2)+t*(n/s)];
				for(int j = t; j < n;j += s){
					int jp = j + bs;
					double re = dstRe[jp]*wRe - dstIm[jp]*wIm;
					double im = dstRe[jp]*wIm + dstIm[jp]*wRe;
					dstRe[jp] = dstRe[j] - re;
					dstIm[jp] = dstIm[j] - im;
					dstRe[j] += re;
					dstIm[j] += im;
				}
			}
		}
		return new double[][]{dstRe, dstIm};
	}

	public static double[][] doFFFT(double[] srcRe, double[] srcIm)
	{
		int n = srcRe.length;
		double[] dstRe = new double[n];
		double[] dstIm = new double[n];

		for(int i = 0;i < n;i++){
			dstRe[i] = srcRe[rev[i]];
			dstIm[i] = srcIm[rev[i]];
		}

		for(int s = 2;s <= n;s <<= 1){
			int nt = s >>> 1;
			int bs = nt;

			for(int t = 0;t < nt;t++){
				double wRe = coss[t*(n/s)];
				double wIm = coss[(n>>>2)+t*(n/s)];
				for(int j = t; j < n;j += s){
					int jp = j + bs;
					double re = dstRe[jp]*wRe - dstIm[jp]*wIm;
					double im = dstRe[jp]*wIm + dstIm[jp]*wRe;
					dstRe[jp] = dstRe[j] - re;
					dstIm[jp] = dstIm[j] - im;
					dstRe[j] += re;
					dstIm[j] += im;
				}
			}
		}
		return new double[][]{dstRe, dstIm};
	}


	public static void main(String[] args) {
		new H().run();
	}

	public void run()
	{
		long S = System.currentTimeMillis();
		is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes());
		out = new FastWriter(System.out);

		solve();
		out.flush();
		long G = System.currentTimeMillis();
		tr(G-S+"ms");
		//		Thread t = new Thread(null, null, "~", Runtime.getRuntime().maxMemory()){
		//			@Override
		//			public void run() {
		//				long s = System.currentTimeMillis();
		//				solve();
		//				out.flush();
		//				if(!INPUT.isEmpty())tr(System.currentTimeMillis()-s+"ms");
		//			}
		//		};
		//		t.start();
		//		t.join();
	}

	private boolean eof()
	{
		if(lenbuf == -1)return true;
		int lptr = ptrbuf;
		while(lptr < lenbuf)if(!isSpaceChar(inbuf[lptr++]))return false;

		try {
			is.mark(1000);
			while(true){
				int b = is.read();
				if(b == -1){
					is.reset();
					return true;
				}else if(!isSpaceChar(b)){
					is.reset();
					return false;
				}
			}
		} catch (IOException e) {
			return true;
		}
	}

	private final byte[] inbuf = new byte[1024];
	public int lenbuf = 0, ptrbuf = 0;

	private int readByte()
	{
		if(lenbuf == -1)throw new InputMismatchException();
		if(ptrbuf >= lenbuf){
			ptrbuf = 0;
			try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); }
			if(lenbuf <= 0)return -1;
		}
		return inbuf[ptrbuf++];
	}

	private boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); }
	//	private boolean isSpaceChar(int c) { return !(c >= 32 && c <= 126); }
	private int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; }

	private double nd() { return Double.parseDouble(ns()); }
	private char nc() { return (char)skip(); }

	private String ns()
	{
		int b = skip();
		StringBuilder sb = new StringBuilder();
		while(!(isSpaceChar(b))){
			sb.appendCodePoint(b);
			b = readByte();
		}
		return sb.toString();
	}

	private char[] ns(int n)
	{
		char[] buf = new char[n];
		int b = skip(), p = 0;
		while(p < n && !(isSpaceChar(b))){
			buf[p++] = (char)b;
			b = readByte();
		}
		return n == p ? buf : Arrays.copyOf(buf, p);
	}

	private char[][] nm(int n, int m)
	{
		char[][] map = new char[n][];
		for(int i = 0;i < n;i++)map[i] = ns(m);
		return map;
	}

	private int[][] nmi(int n, int m)
	{
		int[][] map = new int[n][];
		for(int i = 0;i < n;i++)map[i] = na(m);
		return map;
	}

	private int[] na(int n)
	{
		int[] a = new int[n];
		for(int i = 0;i < n;i++)a[i] = ni();
		return a;
	}

	private long[] nal(int n)
	{
		long[] a = new long[n];
		for(int i = 0;i < n;i++)a[i] = nl();
		return a;
	}

	private int ni()
	{
		int num = 0, b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}

		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}

	private long nl()
	{
		long num = 0;
		int b;
		boolean minus = false;
		while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-'));
		if(b == '-'){
			minus = true;
			b = readByte();
		}

		while(true){
			if(b >= '0' && b <= '9'){
				num = num * 10 + (b - '0');
			}else{
				return minus ? -num : num;
			}
			b = readByte();
		}
	}

	public static class FastWriter
	{
		private static final int BUF_SIZE = 1<<13;
		private final byte[] buf = new byte[BUF_SIZE];
		private final OutputStream out;
		private int ptr = 0;

		private FastWriter(){out = null;}

		public FastWriter(OutputStream os)
		{
			this.out = os;
		}

		public FastWriter(String path)
		{
			try {
				this.out = new FileOutputStream(path);
			} catch (FileNotFoundException e) {
				throw new RuntimeException("FastWriter");
			}
		}

		public FastWriter write(byte b)
		{
			buf[ptr++] = b;
			if(ptr == BUF_SIZE)innerflush();
			return this;
		}

		public FastWriter write(char c)
		{
			return write((byte)c);
		}

		public FastWriter write(char[] s)
		{
			for(char c : s){
				buf[ptr++] = (byte)c;
				if(ptr == BUF_SIZE)innerflush();
			}
			return this;
		}

		public FastWriter write(String s)
		{
			s.chars().forEach(c -> {
				buf[ptr++] = (byte)c;
				if(ptr == BUF_SIZE)innerflush();
			});
			return this;
		}

		private static int countDigits(int l) {
			if (l >= 1000000000) return 10;
			if (l >= 100000000) return 9;
			if (l >= 10000000) return 8;
			if (l >= 1000000) return 7;
			if (l >= 100000) return 6;
			if (l >= 10000) return 5;
			if (l >= 1000) return 4;
			if (l >= 100) return 3;
			if (l >= 10) return 2;
			return 1;
		}

		public FastWriter write(int x)
		{
			if(x == Integer.MIN_VALUE){
				return write((long)x);
			}
			if(ptr + 12 >= BUF_SIZE)innerflush();
			if(x < 0){
				write((byte)'-');
				x = -x;
			}
			int d = countDigits(x);
			for(int i = ptr + d - 1;i >= ptr;i--){
				buf[i] = (byte)('0'+x%10);
				x /= 10;
			}
			ptr += d;
			return this;
		}

		private static int countDigits(long l) {
			if (l >= 1000000000000000000L) return 19;
			if (l >= 100000000000000000L) return 18;
			if (l >= 10000000000000000L) return 17;
			if (l >= 1000000000000000L) return 16;
			if (l >= 100000000000000L) return 15;
			if (l >= 10000000000000L) return 14;
			if (l >= 1000000000000L) return 13;
			if (l >= 100000000000L) return 12;
			if (l >= 10000000000L) return 11;
			if (l >= 1000000000L) return 10;
			if (l >= 100000000L) return 9;
			if (l >= 10000000L) return 8;
			if (l >= 1000000L) return 7;
			if (l >= 100000L) return 6;
			if (l >= 10000L) return 5;
			if (l >= 1000L) return 4;
			if (l >= 100L) return 3;
			if (l >= 10L) return 2;
			return 1;
		}

		public FastWriter write(long x)
		{
			if(x == Long.MIN_VALUE){
				return write("" + x);
			}
			if(ptr + 21 >= BUF_SIZE)innerflush();
			if(x < 0){
				write((byte)'-');
				x = -x;
			}
			int d = countDigits(x);
			for(int i = ptr + d - 1;i >= ptr;i--){
				buf[i] = (byte)('0'+x%10);
				x /= 10;
			}
			ptr += d;
			return this;
		}

		public FastWriter write(double x, int precision)
		{
			if(x < 0){
				write('-');
				x = -x;
			}
			x += Math.pow(10, -precision)/2;
			//		if(x < 0){ x = 0; }
			write((long)x).write(".");
			x -= (long)x;
			for(int i = 0;i < precision;i++){
				x *= 10;
				write((char)('0'+(int)x));
				x -= (int)x;
			}
			return this;
		}

		public FastWriter writeln(char c){ return write(c).writeln(); }
		public FastWriter writeln(int x){ return write(x).writeln(); }
		public FastWriter writeln(long x){ return write(x).writeln(); }
		public FastWriter writeln(double x, int precision){ return write(x, precision).writeln(); }

		public FastWriter write(int... xs)
		{
			boolean first = true;
			for(int x : xs) {
				if (!first) write(' ');
				first = false;
				write(x);
			}
			return this;
		}

		public FastWriter write(long... xs)
		{
			boolean first = true;
			for(long x : xs) {
				if (!first) write(' ');
				first = false;
				write(x);
			}
			return this;
		}

		public FastWriter write(IntUnaryOperator f, int... xs)
		{
			boolean first = true;
			for(int x : xs) {
				if (!first) write(' ');
				first = false;
				write(f.applyAsInt(x));
			}
			return this;
		}

		public FastWriter write(LongUnaryOperator f, long... xs)
		{
			boolean first = true;
			for(long x : xs) {
				if (!first) write(' ');
				first = false;
				write(f.applyAsLong(x));
			}
			return this;
		}

		public FastWriter writeln()
		{
			return write((byte)'\n');
		}

		public FastWriter writeln(int... xs) { return write(xs).writeln(); }
		public FastWriter writeln(long... xs) { return write(xs).writeln(); }
		public FastWriter writeln(IntUnaryOperator f, int... xs) { return write(f, xs).writeln(); }
		public FastWriter writeln(LongUnaryOperator f, long... xs) { return write(f, xs).writeln(); }
		public FastWriter writeln(char[] line) { return write(line).writeln(); }
		public FastWriter writeln(char[]... map) { for(char[] line : map)write(line).writeln();return this; }
		public FastWriter writeln(String s) { return write(s).writeln(); }

		private void innerflush()
		{
			try {
				out.write(buf, 0, ptr);
				ptr = 0;
			} catch (IOException e) {
				throw new RuntimeException("innerflush");
			}
		}

		public void flush()
		{
			innerflush();
			try {
				out.flush();
			} catch (IOException e) {
				throw new RuntimeException("flush");
			}
		}

		public FastWriter print(byte b) { return write(b); }
		public FastWriter print(char c) { return write(c); }
		public FastWriter print(char[] s) { return write(s); }
		public FastWriter print(String s) { return write(s); }
		public FastWriter print(int x) { return write(x); }
		public FastWriter print(long x) { return write(x); }
		public FastWriter print(double x, int precision) { return write(x, precision); }
		public FastWriter println(char c){ return writeln(c); }
		public FastWriter println(int x){ return writeln(x); }
		public FastWriter println(long x){ return writeln(x); }
		public FastWriter println(double x, int precision){ return writeln(x, precision); }
		public FastWriter print(int... xs) { return write(xs); }
		public FastWriter print(long... xs) { return write(xs); }
		public FastWriter print(IntUnaryOperator f, int... xs) { return write(f, xs); }
		public FastWriter print(LongUnaryOperator f, long... xs) { return write(f, xs); }
		public FastWriter println(int... xs) { return writeln(xs); }
		public FastWriter println(long... xs) { return writeln(xs); }
		public FastWriter println(IntUnaryOperator f, int... xs) { return writeln(f, xs); }
		public FastWriter println(LongUnaryOperator f, long... xs) { return writeln(f, xs); }
		public FastWriter println(char[] line) { return writeln(line); }
		public FastWriter println(char[]... map) { return writeln(map); }
		public FastWriter println(String s) { return writeln(s); }
		public FastWriter println() { return writeln(); }
	}

	public static void trnz(int... o)
	{
		for(int i = 0;i < o.length;i++)if(o[i] != 0)System.out.print(i+":"+o[i]+" ");
		System.out.println();
	}

	// print ids which are 1
	public static void trt(long... o)
	{
		Queue<Integer> stands = new ArrayDeque<>();
		for(int i = 0;i < o.length;i++){
			for(long x = o[i];x != 0;x &= x-1)stands.add(i<<6|Long.numberOfTrailingZeros(x));
		}
		System.out.println(stands);
	}

	public static void tf(boolean... r)
	{
		for(boolean x : r)System.out.print(x?'#':'.');
		System.out.println();
	}

	public static void tf(boolean[]... b)
	{
		for(boolean[] r : b) {
			for(boolean x : r)System.out.print(x?'#':'.');
			System.out.println();
		}
		System.out.println();
	}

	public void tf(long[]... b)
	{
		if(INPUT.length() != 0) {
			for (long[] r : b) {
				for (long x : r) {
					for (int i = 0; i < 64; i++) {
						System.out.print(x << ~i < 0 ? '#' : '.');
					}
				}
				System.out.println();
			}
			System.out.println();
		}
	}

	public void tf(long... b)
	{
		if(INPUT.length() != 0) {
			for (long x : b) {
				for (int i = 0; i < 64; i++) {
					System.out.print(x << ~i < 0 ? '#' : '.');
				}
			}
			System.out.println();
		}
	}

	private void tr(Object... o) { if(INPUT.length() != 0)System.out.println(Arrays.deepToString(o)); }
}