Add XCTest at runtime

Amazing.h

#import <Foundation/Foundation.h>
#import "Smiler.h"

@interface Amazing : NSObject <Smiler>

@end

Amazing.m

#import "Amazing.h"

@implementation Amazing

- (BOOL)smile
{
    return NO;
}

@end

Happy.h

#import <Foundation/Foundation.h>
#import "Smiler.h"

@interface Happy : NSObject <Smiler>

@end

Happy.m

#import "Happy.h"

@implementation Happy

- (BOOL)smile
{
    return YES;
}

@end

Smiler.h

#import <Foundation/Foundation.h>

@protocol Smiler <NSObject>

- (BOOL)smile;

@end

testingTests.m

#import <UIKit/UIKit.h>
#import <XCTest/XCTest.h>
#import <objc/runtime.h>
#import "Smiler.h"

@interface testingTests : XCTestCase

@end

@implementation testingTests

+ (void)initialize
{
    Class metaclass = self.class;
    BOOL success = class_addMethod(metaclass, @selector(testRuntime), (IMP)runtimeSmilerTest, "v@:");

    NSLog(@"------------ Added %d", success);
}

void
runtimeSmilerTest(id self, SEL _cmd) {
    NSArray *classes = [testingTests findClassesConformingToProtocol:@protocol(Smiler)];
    NSLog(@"Smiler classes: %@", classes);
    
    for (Class class in classes) {
        id<Smiler> smiler = [[class alloc] init];
        NSLog(@"|||||||||||||| Runtime test! %@", class);
        XCTAssert([smiler smile], @"Fake! Pass");
    }
}

+ (NSArray *)findClassesConformingToProtocol:(Protocol *)protocol
{
    int numberOfClasses = objc_getClassList(NULL, 0);
    Class *classes;
    
    classes = (Class *)malloc(sizeof(Class) * numberOfClasses);
    objc_getClassList(classes, numberOfClasses);
    
    NSMutableArray *conformingClasses = [NSMutableArray array];
    for (NSInteger i = 0; i < numberOfClasses; i++) {
        Class lClass = classes[i];
        if (class_conformsToProtocol(lClass, protocol)) {
            [conformingClasses addObject:classes[i]];
        }
    }
    
    free(classes);
    return [conformingClasses copy];
}

- (void)setUp {
    [super setUp];
}

- (void)tearDown {
    [super tearDown];
}

- (void)testExample {
    // This is an example of a functional test case.
    XCTAssert(YES, @"Pass");
}