Why does initWithCoder: return the wrong object class during object decoding?

Question

I'm attempting to use NSKeyedArchiver / NSKeyedUnarchiver in a trivial test case and observing that when initWithCoder: is called, the object that is created reports that it has the wrong class.

TestCoder.h

#import <Foundation/Foundation.h>

@interface TestCoder : NSObject <NSCoding>

@end

TestCoder.m

#import "TestCoder.h"

@implementation TestCoder

- (id)initWithCoder:(NSCoder *)aDecoder {
    self = [super init];

    NSLog(@"TestCoder is a kind of of TestCoder? %@", [self isKindOfClass:TestCoder.class] ? @"YES" : @"NO");

    return self;
}

- (void)encodeWithCoder:(NSCoder *)aCoder {
    [aCoder encodeObject:@"Test"];
}

@end

NSLog outputs:

2015-07-22 14:10:45.394 TestCoder[10858:632647] TestCoder is a kind of of TestCoder? YES

When I unit test this, however, it doesn't seem to work.

#import <UIKit/UIKit.h>
#import <XCTest/XCTest.h>
#import "TestCoder.h"

@interface TestCoderTests : XCTestCase

@end

@implementation TestCoderTests

- (void)testExample {
    NSData *data = [NSKeyedArchiver archivedDataWithRootObject:[TestCoder new]];

    TestCoder *object = [NSKeyedUnarchiver unarchiveObjectWithData:data];
    XCTAssert([object isKindOfClass:TestCoder.class]);
}

@end

My test case reports:

error: -[TestCoderTests testExample] : (([object isKindOfClass:TestCoder.class]) is true) failed

But when I inspect the object's class using the debugger I get results that contradict my test case:

(lldb) po [object isKindOfClass:TestCoder.class]
true

What is going on here?

I can see that I'm not misusing isKindOfClass by using a simple test case that passes.

- (void)testClassEquality {
    TestCoder *object = [TestCoder new];
    XCTAssert([object isKindOfClass:TestCoder.class]);
}

Is there some trick to get NSCoder to work properly that I can't find in the documentation?