#include<bits/stdc++.h>
#define ll	long long
using namespace std;
#define N  100005

ll dp[N][2];
ll c1, c2, n;
string s;

ll fun(ll i, bool f) {
	if(i == n) {
		return 0;
	}
	ll& ans = dp[i][f];
	if(ans != -1) {
		return ans;
	}
	if(f) {
		if(s[i] == 'B') {
			ans = min(fun(i + 1, 1) + c2, fun(i + 1, 0));
		} else {
			ans = fun(i + 1, 1);
		}
	} else {
		if(s[i] == 'B') {
			ans = fun(i + 1, 0);
		} else {
			ans = fun(i + 1, 1) + c1;
		}
	}
	return ans;
}


void solve()
{
	cin >> c1 >> c2 >> s;
	n = s.length();	
	for(int i = 0; i <= n; i++) {
		for(int j = 0; j < 2; j++) {
			dp[i][j] = -1;
		}
	}
	ll ans;
	if(s[0] == 'W') {
		ans = fun(1,1) + c1;
	} else {
		ans = fun(1,0);
	}
	cout << ans << endl;
	return;
}
int main()
{
	int TESTS=1;
	cin >> TESTS;
	while(TESTS -- )
	{
        solve();
    }
	return 0;
}