Manipulate different function and variable

Question

I have list of functions such that

test = {test1[a,x], test2[a,x], test3[a,x]};

I would like to plot this three function using manipulation

Manipulate[Plot[test[[i]],{x,0,1}],
,{i,{1,2,3}},{a,0,1}]

So I want to generate the function by selecting i, but actually it does not respond the manipulate. How shall I solve the issue?

Example

f1[x_, x1_] := x^2 + x1^2
f2[x_, x1_] := x^3 + x1
f3[x_, x1_] := x + x1
ftest = {f1[x, x1], f2[x, x1], f3[x, x1]};
Manipulate[Plot[ftest[[i]], {x, -1, 1}], {i, {1, 2, 3}}, {x1, 0, 10}]

Answer 1

f1[x_, x1_] := x^2 + x1^2
f2[x_, x1_] := x^3 + x1
f3[x_, x1_] := x + x1
ftest = {f1, f2, f3};
Manipulate[Plot[ftest[[i]][x, x1], {x, -1, 1}], {i, {1, 2, 3}}, {x1, 0, 10}]

Alternatively, without having to define ftest:

Manipulate[Plot[f[x, x1], {x, -1, 1}], {f, {f1, f2, f3}}, {x1, 0, 10}]