Implementation of an XCTestExpectation for delegate calls. More here http://www.ashton-w.net/2016/01/23/Asynchronous-Testing.html

ExpectationDelegateProxy.h

#import <Foundation/Foundation.h>
#import <XCTest/XCTest.h>

NS_ASSUME_NONNULL_BEGIN

@interface ExpectationDelegateProxy : NSProxy

@property (nonatomic) SEL selector;
@property (nonatomic) Protocol *protocol;
@property (nonatomic) XCTestExpectation *expectation;

- (instancetype)initWithProtocol:(Protocol *)protocol selector:(SEL)selector expectation:(XCTestExpectation *)expectation;

@end

NS_ASSUME_NONNULL_END

ExpectationDelegateProxy.m

#import "ExpectationDelegateProxy.h"
#import <objc/runtime.h>
#import <objc/protocol.h>

@implementation ExpectationDelegateProxy

- (instancetype)initWithProtocol:(Protocol *)protocol selector:(SEL)selector expectation:(XCTestExpectation *)expectation
{
    NSParameterAssert(protocol);
    NSParameterAssert(selector);
    NSParameterAssert(expectation);
    
    _protocol = protocol;
    _selector = selector;
    _expectation = expectation;
    
    return self;
}

#pragma mark - NSProxy

- (void)forwardInvocation:(NSInvocation *)invocation
{
    if (sel_isEqual(self.selector, invocation.selector)) {
        [self.expectation fulfill];
    }
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)aSelector
{
    // taken from OCMock's OCProtocolMockObject
    struct { BOOL isRequired; BOOL isInstance; } opts[4] = { {YES, YES}, {NO, YES}, {YES, NO}, {NO, NO} };
    for(int i = 0; i < 4; i++)
    {
        struct objc_method_description methodDescription = protocol_getMethodDescription(self.protocol, aSelector, opts[i].isRequired, opts[i].isInstance);
        if(methodDescription.name != NULL)
            return [NSMethodSignature signatureWithObjCTypes:methodDescription.types];
    }
    return nil;
}

- (BOOL)conformsToProtocol:(Protocol *)aProtocol
{
    return protocol_conformsToProtocol(self.protocol, aProtocol);
}

- (BOOL)respondsToSelector:(SEL)selector
{
    return ([self methodSignatureForSelector:selector] != nil);
}

- (BOOL)isKindOfClass:(Class)aClass
{
    return (self.class == aClass);
}

@end

XCTestCase+DelegateExpectation.swift

import XCTest
import ObjectiveC.runtime

var ExpectationDelegateProxyAssociationKey: UInt8 = 0

extension XCTestExpectation {
    var delegateProxy: ExpectationDelegateProxy {
        get {
            return objc_getAssociatedObject(self, &ExpectationDelegateProxyAssociationKey) as! ExpectationDelegateProxy
        }
        set {
            objc_setAssociatedObject(self, &ExpectationDelegateProxyAssociationKey, newValue, objc_AssociationPolicy.OBJC_ASSOCIATION_RETAIN_NONATOMIC)
        }
    }
}

extension XCTestCase {
    
    func expectationForDelegate(delegate: Protocol, selector: Selector) -> XCTestExpectation {
        
        let expectation = expectationWithDescription("\(selector) called on \(NSStringFromProtocol(delegate))")
        expectation.delegateProxy = ExpectationDelegateProxy(withProtocol: delegate, selector: selector, expectation: expectation);
        
        return expectation;
    }
    
}