function isApprox( t, actual, expected, rtol ) {
	var delta;
	var tol;

	if ( actual === expected ) {
		t.strictEqual( actual, expected, 'returns expected value' );
	} else {
		delta = abs( actual - expected );
		tol = rtol * EPS * abs( expected );
		t.ok( delta <= tol, 'within tolerance. actual: '+actual+'. expected: '+expected+'. delta: '+delta+'. tol: '+tol+'.' );
	}
}
Tests for element-wise approximate equality.

@private
@param {Object} t - test object
@param {number} actual - actual value
@param {number} expected - expected value
@param {number} rtol - relative tolerance