#include <bits/stdc++.h>
#define pb push_back
#define ll long long
//   cout<<"Case #"<<t1-t<<": "<<ans<<"\n";
using namespace std;
/*bool cmp(vector<int>:: iterator it1,vector<int>:: iterator it2)
{
    if(*it1>*it2)
    return true;
    else
    return false; 
}*/
/*bool cmp(int a, int b)
{
    if(abs(a)>abs(b))
    return true;
    else
    return false;
}*/
/*ll int gcd(ll int a,ll int b)
{
    if(a==0)
    return b;
    else return gcd(b%a,a);
}*/
/*bool cmp(pair<int,int> p1,pair<int,int> p2)
{
    if(p1.first<p2.first)
    return true;
    else if(p1.first==p2.first)
    {
        if(p1.second<p2.second)
        return true;
        else
        return false;
    }
    else
    return false;
}
*/
/*vector<int> dp(1000000001,-1);
ll int knapsack(ll int wt[],ll int val[],ll int W,ll int n)
{
    if(W==0||n==0)
    return 0;
    if(dp[n][W]!=-1)
    return dp[n][W];
    if(wt[n-1]<=W)
    {
        dp[n][W] = max(val[n-1]+knapsack(wt,val,W-wt[n-1],n-1),knapsack(wt,val,W,n-1));
        return dp[n][W];
    }
    dp[n][W] = knapsack(wt,val,W,n-1);
    return dp[n][W];
}*/
int main() {     
    /* #ifndef
     //For getting input from input.txt file                                
   freopen("input.txt", "r", stdin); 
    // Printing the Output to output.txt file 
    freopen("output.txt", "w", stdout); 
    #endif*/
   // memset(dp,-1,sizeof(dp));
    //int t;
    //cin>>t;
   // while(t--)
   int t;
   cin>>t;
   while(t--)
   {
      int n,k;
      string a,b;
      cin>>n>>k>>a>>b;
      int a1[26]={0};
      int b1[26]={0};
      for(int i=0;i<n;i++)
      {
          a1[a[i]-'a']++;
          b1[b[i]-'a']++;
      }
      bool ans=true;
    for(int i=0;i<25;i++)
    {
        if(a1[i]<b1[i])
            {
                ans=false;
                break;
            }
            else
            {
                if((b1[i]-a1[i])%k)
                {
                ans=false;
                break;
                }
                b1[i+1]+=b1[i]-a1[i];
            }
    }
    cout<< (ans ? "Yes" : "No") <<"\n";
       
   }
   
return 0;
}