public class AnimalLocator
{    
    public static string getAnimalNameById(Integer id)
    {
        Http http = new Http();
        HttpRequest request = new HttpRequest();
        request.setEndpoint('https://th-apex-http-callout.herokuapp.com/animals/'+id);
        request.setMethod('GET');
        HttpResponse response = http.send(request);
        system.debug(response.getBody());
        // If the request is successful, parse the JSON response.
        if (response.getStatusCode() == 200) 
        {
            // Deserialize the JSON string into collections of primitive data types.
            Map<String, Object> results = (Map<String, Object>) JSON.deserializeUntyped(response.getBody());
            system.debug(results);
            // Cast the values in the 'animals' key as a list
            Map<String, Object> animals = (Map<String, Object>) results.get('animal');
            system.debug(animals);
            System.debug('Received the following animals:');
            //System.debug(animals);
            System.debug(animals.get('name'));
            return (String)animals.get('name');
		}
          return null;
    }

}

@isTest
global class AnimalLocatorMock implements HttpCalloutMock {
     // Implement this interface method
    global HTTPResponse respond(HTTPRequest request) {
        // Create a fake response
        HttpResponse response = new HttpResponse();
        response.setHeader('Content-Type', 'application/json');
        response.setBody('{"animal":{"id":1,"name":"bear","eats":"berries, campers, adam seligman","says":"yum yum"}}');
        response.setStatusCode(200);
        return response; 
    }
}

@isTest
global class AnimalLocatorMockFail implements HttpCalloutMock {
     // Implement this interface method
    global HTTPResponse respond(HTTPRequest request) {
        // Create a fake response
        HttpResponse response = new HttpResponse();
        response.setHeader('Content-Type', 'application/json');
        response.setBody('{"animal":{"id":1123123123,"name":"bear","eats":"berries, campers, adam seligman","says":"yum yum"}}');
        response.setStatusCode(201);
        return response; 
    }
}

@isTest
private class AnimalLocatorTest{
    @isTest static void AnimalLocatorMock1() {
        Test.setMock(HttpCalloutMock.class, new AnimalLocatorMock());
        string result = AnimalLocator.getAnimalNameById(1);
        String expectedResult = 'bear';
        System.assertEquals(result,expectedResult);
    }
    @isTest static void AnimalLocatorMock2() {
        Test.setMock(HttpCalloutMock.class, new AnimalLocatorMockFail());
        string result = AnimalLocator.getAnimalNameById(123456789);
        String expectedResult = 'bear2';
        System.assertEquals(result,expectedResult);
    }
}