How to read in a local JSON file for testing

Question

I'm trying to write unit tests for json validation (since the app heavily relies on json from a rest API).

I have a local file that contains simple json: "goodFeaturedJson.txt"

The contents:

{
  "test": "TEST"
}

The test case:

- (void)testJsonIsValid
{
    Featured *featured = [Featured new];

    NSString* filepath = [[NSBundle mainBundle]pathForResource:@"goodFeaturedJson" ofType:@"text"];

    NSData *data = [NSData dataWithContentsOfFile:filepath];

    NSString *jsonString = [[NSString alloc] initWithContentsOfFile:filepath encoding:NSUTF8StringEncoding error:nil];//[[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

    NSLog(@"The json string is: %@", jsonString);

    id JSON = [NSJSONSerialization JSONObjectWithData:data options:kNilOptions error:nil];

    STAssertTrue([featured jsonIsValid:JSON], @"Featured Data is NOT valid...");    
}

The test fails every time. The console prints:

The json string is: (null)

Why? I know why the test is failing, since clearly if the data is nil/null there will be no valid json, and the validator will break (which it should if its invalid).

There must be something simple I missed here, any ideas?

Answer 1

In a unit test you probably want to use [NSBundle bundleForClass:[self class]], and not [NSBundle mainBundle]. That's because the unit test is not a standalone app. With mainBundle you get something like /Applications/Xcode.app/Contents/Developer/Tools, but using bundleForClass gets you the bundle where your unit test class is located.

guard let pathString = Bundle(for: type(of: self)).path(forResource: "UnitTestData", ofType: "json") else {
    fatalError("UnitTestData.json not found")
}

Answer 2

In Swift

Swift 5 and above

guard let pathString = Bundle(for: type(of: self)).path(forResource: "UnitTestData", ofType: "json") else {
    fatalError("UnitTestData.json not found")
}

guard let jsonString = try? String(contentsOfFile: pathString, encoding: .utf8) else {
    fatalError("Unable to convert UnitTestData.json to String")
}

print("The JSON string is: \(jsonString)")

guard let jsonData = jsonString.data(using: .utf8) else {
    fatalError("Unable to convert UnitTestData.json to Data")
}

guard let jsonDictionary = try? JSONSerialization.jsonObject(with: jsonData, options: []) as? [String:Any] else {
    fatalError("Unable to convert UnitTestData.json to JSON dictionary")
}

print("The JSON dictionary is: \(jsonDictionary)")

Swift 3 and 4

guard let pathString = Bundle(for: type(of: self)).path(forResource: "UnitTestData", ofType: "json") else {
    fatalError("UnitTestData.json not found")
}

guard let jsonString = try? NSString(contentsOfFile: pathString, encoding: String.Encoding.utf8.rawValue) else {
    fatalError("Unable to convert UnitTestData.json to String")
}

print("The JSON string is: \(jsonString)")

guard let jsonData = jsonString.data(using: String.Encoding.utf8.rawValue) else {
    fatalError("Unable to convert UnitTestData.json to NSData")
}

guard let jsonDictionary = try? JSONSerialization.jsonObject(with: jsonData, options: []) as? [String:AnyObject] else {
    fatalError("Unable to convert UnitTestData.json to JSON dictionary")
}

print("The JSON dictionary is: \(jsonDictionary)")

Swift 2.2

    guard let pathString = NSBundle(forClass: self.dynamicType).pathForResource("UnitTestData", ofType: "json") else {
        fatalError("UnitTestData.json not found")
    }

    guard let jsonString = try? NSString(contentsOfFile: pathString, encoding: NSUTF8StringEncoding) else {
        fatalError("Unable to convert UnitTestData.json to String")
    }

    print("The JSON string is: \(jsonString)")

    guard let jsonData = jsonString.dataUsingEncoding(NSUTF8StringEncoding) else {
        fatalError("Unable to convert UnitTestData.json to NSData")
    }

    guard let jsonDictionary = try? NSJSONSerialization.JSONObjectWithData(jsonData, options: []) as? [String:AnyObject] else {
        fatalError("Unable to convert UnitTestData.json to JSON dictionary")
    }

    print("The JSON dictionary is: \(jsonDictionary)")

*This incorporates Tom Harrington's answer which is in Objective C