cocoa - Why can't code inside unit tests find bundle resources?

Question

Some code I am unit testing needs to load a resource file. It contains the following line:

NSString *path = [[NSBundle mainBundle] pathForResource:@"foo" ofType:@"txt"];

In the app it runs just fine, but when run by the unit testing framework pathForResource: returns nil, meaning it could not locate foo.txt.

I've made sure that foo.txt is included in the Copy Bundle Resources build phase of the unit test target, so why can't it find the file?

Answer 1

When the unit test harness runs your code, your unit test bundle is NOT the main bundle.

Even though you are running tests, not your application, your application bundle is still the main bundle. (Presumably, this prevents the code you are testing from searching the wrong bundle.) Thus, if you add a resource file to the unit test bundle, you won't find it if search the main bundle. If you replace the above line with:

NSBundle *bundle = [NSBundle bundleForClass:[self class]];
NSString *path = [bundle pathForResource:@"foo" ofType:@"txt"];

Then your code will search the bundle that your unit test class is in, and everything will be fine.