Controller making request to an external API
After running the code through JSHint, you are missing a semicolon on line 16 of the first code swatch (], cb)). The tests look good on JSHint.

I suggest making the following changes:

Remove async.waterfall in getFixture

As you said in your own words, "performance isn't really an issue". As such, I'd recommend to just remove the waterfall function to make the code cleaner and easier to maintain. You probably won't run into a noticeable speed difference anyways, if it is on cron.

Shorten callbacks

This may be more opinionated, but I would suggest in the first swatch to change your callbacks from this format:

var errorMsg = "Error in response with code: " + response.statusCode;
callback(null, errorMsg);


to this format:

callback(null, "Error in response with code: " + response.statusCode);


It is just as easy to read (if not easier) and works just the same, except without the variable instantiation.

Shorten a line

function getFixture(cb) {...
module.exports = getFixture;


Change to

module.exports = function(cb) {...


Or, even (according to choice):

module.exports = function getFixture(cb) {...


Good luck!