How to test a simple data object class which implements NSCoding? - ios

Question

I have a small data object that needs to be serialized and deserialized. Lets say it is called WeatherDetails, and it looks like this:
WeatherDetails.h
#interface WeatherDetails : NSObject <NSCoding>
{
#private
#protected
}
#pragma mark - Properties
#property (nonatomic, copy) NSString *weatherCode;
#property (nonatomic, copy) NSString *weatherDescription;
#end
WeatherDetails.m
#import "WeatherDetails.h"
#implementation WeatherDetails
NSString *const WEATHER_DETAILS_WEATHER_CODE_KEY = #"s";
NSString *const WEATHER_DETAILS_WEATHER_DESCRIPTION_KEY = #"sT";
#pragma mark - Initialization, NSCoding and Dealloc
- (instancetype)initWithCoder:(NSCoder *)aDecoder
{
self = [super init];
_weatherCode = [aDecoder decodeObjectForKey:#"weatherCode"];
_weatherDescription = [aDecoder decodeObjectForKey:#"weatherDescription"];
return self;
}
- (void)encodeWithCoder:(NSCoder *)aCoder
{
[aCoder encodeObject:_weatherCode forKey:#"weatherCode"];
[aCoder encodeObject:_weatherDescription forKey:#"weatherDescription"];
}
Currently my tests look like this;
#import <XCTest/XCTest.h>
#import <OCMock/OCMock.h>
#import "WeatherDetails.h"
#interface WeatherDetailsTests : XCTestCase
#end
#implementation WeatherDetailsTests
- (void)testThatWeatherCodeIsEncoded
{
WeatherDetails *details = [[WeatherDetails alloc] init];
[details setWeatherCode:#"A"];
NSData *archive = [NSKeyedArchiver archivedDataWithRootObject:details];
WeatherDetails *unarchive = [NSKeyedUnarchiver unarchiveObjectWithData:archive];
XCTAssertEqualObjects(#"A", [unarchive weatherCode]);
}
- (void)testThatWeatherDescriptionIsEncoded
{
WeatherDetails *details = [[WeatherDetails alloc] init];
[details setWeatherDescription:#"A"];
NSData *archive = [NSKeyedArchiver archivedDataWithRootObject:details];
WeatherDetails *unarchive = [NSKeyedUnarchiver unarchiveObjectWithData:archive];
XCTAssertEqualObjects(#"A", [unarchive weatherDescription]);
}
I have a gut feeling that this approach to testing if all properties are correctly encoded is not really optimal as there is duplication, but I can't really think of a better approach. Does anyone have a tip for me on improving this?

Answer 1

What you really want to test is that the object is same before and after you archive it.
Implement a method in your WeatherDetails to compare the objects (or override isEqual:).
- (BOOL)isEqualToWeatherDetails:(WeatherDetails *)details
{
if (![details isKindOfClass:[WeatherDetails class]]) return NO;
return [self.weatherCode == details.weatherCode && self.weatherDescription isEqualToString:details.weatherDescription];
}
Then you can do all your equality comparisons at once:
- (void)testNSCoder
{
WeatherDetails *details = [[WeatherDetails alloc] init];
[details setWeatherCode:#"A"];
details.weatherDescription = #"Cloudy";
NSData *archive = [NSKeyedArchiver archivedDataWithRootObject:details];
WeatherDetails *unarchive = [NSKeyedUnarchiver unarchiveObjectWithData:archive];
XCTAssertTrue([details isEqualToWeatherDetails:unarchive]);
}
If you overrode isEqual: then you could compare doing this:
XCTAssertEqualObjects(details, unarchive);
Apple tends to add additional methods (isEqualToArray:, isEqualToDictionary:). isEqual: is used by collections like NSSet and NSDictionary

Answer 2

In the end I improved it by applying a custom assertion;
When To Use It
We should consider creating a Custom Assertion whenever any of the following are true:
We find ourselves writing (or cloning) the same assertion logic in test after test
We find ourselves writing Conditional Test Logic in the result verification part of our tests. That is, our calls to Assertion Methods are embedded in if statements or loops.
The result verification parts of our tests are suffering from Obscure Test because we are using procedural rather than declarative result verification in the tests.
We find ourselves doing Frequent Debugging whenever assertions fail because they do not provide enough information.
The custom assertion currently looks like this:
/*!
* #define XCTAssertEqualSerialized(value, object, selector)
* Serializes (\a object), then desirializes it and compares result's property (\a propertyName) to (\a value) with XCTAssertEqualObjects
* #param value Value to compare.
* #param object Object to serialize.
* #param selector Objects property to compare.
*/
#define XCTAssertEqualSerialized(value, object, selector) \
({ \
NSData *archived = [NSKeyedArchiver archivedDataWithRootObject:object]; \
NSObject *unarchived = [NSKeyedUnarchiver unarchiveObjectWithData:archived]; \
XCTAssertEqualObjects(value, [unarchived valueForKeyPath:NSStringFromSelector(selector)]); \
})
/*!
* #define XCTAssertNotNilSerialized(object, selector)
* Serializes (\a object), then desirializes it and checks result's property (\a propertyName) is not nil with XCTAssertNotNil
* #param object Object to serialize.
* #param selector Objects property to compare.
*/
#define XCTAssertNotNilSerialized(object, selector) \
({ \
NSData *archived = [NSKeyedArchiver archivedDataWithRootObject:object]; \
NSObject *unarchived = [NSKeyedUnarchiver unarchiveObjectWithData:archived]; \
XCTAssertNotNil([unarchived valueForKeyPath:NSStringFromSelector(selector)]); \
})
Which results in the tests looking like this:
- (void)testThatWeatherCodeIsEncoded
{
WeatherDetails *details = [[WeatherDetails alloc] init];
[details setWeatherCode:#"A"];
XCTAssertEqualSerialized(#"A", details, #selector(weatherCode));
}
- (void)testThatWeatherDescriptionIsEncoded
{
WeatherDetails *details = [[WeatherDetails alloc] init];
[details setWeatherDescription:#"A"];
XCTAssertEqualSerialized(#"A", details, #selector(weatherDescription));
}