test.html

<template name="helper_test">
  {{#each test_objects}}
    <p>Object: {{helper-test this}}</p>
  {{/each}}
</template>

test.js

Handlebars.registerHelper('helper-test', function(object) {
  console.log('object:', object); //this does get called but doesn't return a, b and c like I would expect
  //do some other stuff here
});

Template.helper_test.test_objects = function() {
  return ['a', 'b', 'c'];
}