QA Unary function chainer (UA)

Write tests for a higher order function chainer for chaining together a list of unary functions. In other words, it should return a function that does a left fold on the given functions.

chainer([a,b,c,d])(input) === d(c(b(a(input))));

Example:

function f1(x) {return x * 2};
function f2(x) {return x + 2};
function f3(x) {return Math.pow(x, 2)};

chainer([f1, f2, f3])(0) === 4;

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