Reactive Programming with RxJS/

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Writing a Real-world Test

Writing a Real-world Test

Get familiar with writing a real-world test.

We'll cover the following...

There’s no better way to understand how to bend time using virtual time than to write a test for a time-sensitive task in the real world. Let’s recover an Observable from the earthquake viewer we made earlier.

Javascript (babel-node)
quakes
.pluck('properties')
.map(makeRow)
.bufferWithTime(500)
.filter(function(rows) 
{ 
  return rows.length > 0; 
}) 
.map(function(rows) 
{
  var fragment = document.createDocumentFragment(); 
  rows.forEach(function(row) 
  {
      fragment.appendChild(row);
  });
  return fragment; 
})
.subscribe(function(fragment) 
{ 
  table.appendChild(fragment);
});

To make the code more testable, let’s encapsulate the Observable in a function that takes a Scheduler we use in the bufferWithTime operator. It’s always a good idea to parameterize Schedulers in Observables that will be tested.

Javascript (babel-node)
function quakeBatches(scheduler) 
{ 
  return quakes.pluck('properties')
  .bufferWithTime(500, null, scheduler || null) 
  .filter(function(rows) 
  {
    return rows.length > 0; 
  });
}

Let’s also simplify the code by taking some steps out, but retaining the essence of it. This code takes an Observable of JSON objects that contain a properties property, buffers them into batches released every 500 milliseconds, and filters the batches that arrive empty.

We want to verify that this code works, but ...