#pragma GCC optimize("Ofast")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("avx2")
#define _CRT_SECURE_NO_WARNINGS
#define debug(x) cerr<<" smotri huinyi : "<<#x<<' '<<x<<'\n';
#include "bits/stdc++.h"
//#include "geometry.h"
//#include "data_structure.h"
using namespace std;
using namespace chrono;
#define all(a) a.begin(), a.end()
#define allr(a) a.rbegin(), a.rend()
#define sqrt(x) sqrtl(x)
mt19937 rnd(std::chrono::high_resolution_clock::now().time_since_epoch().count());
typedef long long ll;
typedef long double ld;
signed main() {
#ifdef _DEBUG
    freopen("input.txt", "r", stdin);
    freopen("output.txt", "w", stdout);
#endif
    srand(time(NULL));
    ll t = 1;
    cin >> t;
    while (t--) {
        ll n, m, b, w;
        cin >> n >> m >> b >> w;
        vector<vector<char>> a(4 * n, vector<char>(4 * m));
        a[0][0] = 'B';
        for (ll i = 0; i < 4 * n; i++){
            for (ll j = 0; j < 4 * m; j++){
                a[i][j] = 'B';
                if (i != 0 && a[i - 1][j] == 'B'){
                    a[i][j] = 'W';
                }
                if (j != 0 && a[i][j - 1] == 'B'){
                    a[i][j] = 'W';
                }
            }
        }

        ll cntb = 0, cntw = 0;
        vector<vector<bool>>used(4 * n, vector<bool>(4 * m, 0));
        if (b == 0) {
            if (w != 0) {
                used[0][1] = true;
            }
            for (ll i = 0; i < 4 * n; i++) {
                for (ll j = 0; j < 4 * m; j++) {
                    if (used[i][j]){
                        cout << a[i][j];
                    }
                    else{
                        cout << '.';
                    }
                }
                cout << '\n';
            }
            continue;
        }
        a[1][4 * m - 1] = '.';
        for (int i = 1; i < 4 * m - 2; i++){
            if (cntb == b)
                break;
            if (a[1][i] == 'B'){
                cntb++;
                used[1][i] = true;
            }
            else{
                cntw++;
                used[1][i] = true;
            }
        }
        for (ll i = 2; i < 4 * n - 2; i++) {
            for(ll j = 1; j < 4 * m - 2; j += 4) {
                if (cntw < w && !used[i][j] && a[i][j] == 'W' && a[i - 1][j] == 'B' && used[i - 1][j]) {
                    cntw++;
                    used[i][j] = true;
                }
                if (cntb < b && !used[i][j] && a[i][j] == 'B' && a[i - 1][j] == 'W' && used[i - 1][j]) {
                    cntb++;
                    used[i][j] = true;
                }
            }
        }

        for (ll i = 0; i < 4 * n; i++) {
            for (ll j = 0; j < 4 * m; j++) {
                if (!used[i][j] && a[i][j] == 'B'){
                    used[i][j] = true;
                    a[i][j] = '.';
                }
            }
        }
        for (ll i = 0; i < 4 * n; i++) {
            for (ll j = 0; j < 4 * m; j++) {
                if (!used[i][j]) {
                    bool ok = false;
                    if (i >= 0 && a[i - 1][j] == 'B'){
                        cntw++;
                        used[i][j] = true;
                        ok = true;
                        if (cntw == w)
                            goto print;
                    }
                    if (!ok && j >= 0 && a[i][j - 1] == 'B') {
                        cntw++;
                        used[i][j] = true;
                        ok = true;
                        if (cntw == w)
                            goto print;
                    }
                    if (!ok && j + 1 < 4 * m && a[i][j + 1] == 'B' ){
                        cntw++;
                        used[i][j] = true;
                        ok = true;
                        if (cntw == w)
                            goto print;
                    }
                    if (!ok && i + 1 < 4 * n && a[i + 1][j] == 'B') {
                        cntw++;
                        used[i][j] = true;
                        ok = true;
                        if (cntw == w)
                            goto print;
                    }
                }
            }
        }
print:
        for (ll i = 0; i < 4 * n; i++) {
            for (ll j = 0; j < 4 * m; j++) {
                if (used[i][j])
                    cout << a[i][j];
                else
                    cout << '.';
            }
            cout << '\n';
        }
    }
}