Making NSTimeZone Trouble Free in Unit Tests

Question

So here's the problem with doing unit tests of calendar code in Objective-C: the Timezone contains the information about daylight savings, so you write a test in the summer, expecting sunrise on June 10th to occur at 6:02 am. Your test passes, later, you are running the test when it's not DST and you get a failure, because when you get the timezone, daylightsavings is turned off.

There doesn't seem to be a simple way to just tell it to give you the timezone with dst turned on?

I was thinking about doing a category so that I would intercept the timezone call but that sounds super messy as I don't know what date you are manipulating.

Of course, I could write all my tests to check the timezone setting and then just shift all my expectations but that sounds like the worst of all possible choices.

Answer 1

Region-specific timezones must take into account daylight saving time in order to accurately calculate intervals between two dates (and times). If you aren't interested in this, perhaps you could use a UTC “timezone” instead, which don't change at all.

For example, New Zealand Standard Time is defined as UTC+12:00, and New Zealand Daylight Saving Time is defined as UTC+13:00. Although the local time in New Zealand differs during Daylight Saving Time, the times in UTC+12:00 remain the same (that is, every other country that also uses UTC+12:00 don't magically move forward just because Daylight Saving Time has commenced in New Zealand).

You can achieve this simply by providing that UTC offset as the name:

NSTimeZone *utc_plus12 = [NSTimeZone timeZoneWithName:@"UTC+12:00"];

Find out what UTC offset your region's daylight saving time is based on and use that.

Answer 2

I encountered the similar problem. Finally I found OCMock and saved my life.
If you are using Cocoapods, that will be great! Here is the steps:

1. Edit your Podfile and add a lines to import OCMock.

   target 'YourProjectTests' do
       pod 'OCMock'
   end
   

2. Add import in your unit test class

   #import <OCMock/OCMock.h>
   

3. Write your test case like this

   - (void)testLocalTimezoneFromPDT {
       NSTimeZone* timeZone = [NSTimeZone timeZoneWithAbbreviation:@"PDT"];
       id timeZoneMock = OCMClassMock([NSTimeZone class]);
       OCMStub([timeZoneMock localTimeZone]).andReturn(timeZone);
   
       // Implement your test case
       // XCTAssertEqual(...);
   }
   

That code will mock the original [NSTimeZone localTimeZone] method and return the static value.
In this example, we return the timezone from Pacific Daylight Time (PDT) [GMT-07:00].
When your class call [NSTimeZone localTimeZone], your class will get the timezone we set with OCMock.

Hopes this answer will help you.