Unit test for method block that will occur daily

Question

I have a method Fetch, GetExchangeRate and method FetchOnDemand. FetchOnDemand checkds if Fetch is not called during one day it calls it.

GetExchangeRate calls FetchOnDemand first then does its particular job.

How can I test a FetchOnDemand.

Answer 1

I assume you are asking how to test code that is time-dependent.

One strategy is to refactor the code under test so that you control the definition of the current time. For example, in Java, instead of calling System.currentTimeMillis(), you might call a method on a "time provider" interface. The default to implementation of that interface would call System.currentTimeMillis(). For test purposes, you would use a test implementation that would return a time that you would control.

Another strategy is to provide a way to override your reference time. Suppose your code looks like this:

Fetch() {
    fetch something;
    lastFetchTime = current time;
}

FetchOnDemand() {
   if (lastFetchTime is at least a day ago) {
      Fetch();
   }
}

If you add a SetLastFetchTime() method, your test can control lastFetchTime.

Answer 2

This is a great article on the subject that I've found very comprehensive and helpful. It's great for starting the conversation with your development team to make these sorts of things more test-friendly.

Eradicating Non-Determinism in Tests