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XCTestObservationCenter+Register.m
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XCTestObservationCenter+Register.m
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#import <XCTest/XCTest.h>
#import <objc/runtime.h>
#if __has_include("Nimble-Swift.h")
#import "Nimble-Swift.h"
#else
#import <Nimble/Nimble-Swift.h>
#endif
#pragma mark - Method Swizzling
/// Swaps the implementations between two instance methods.
///
/// @param class The class containing `originalSelector`.
/// @param originalSelector Original method to replace.
/// @param replacementSelector Replacement method.
void swizzleSelectors(Class class, SEL originalSelector, SEL replacementSelector) {
Method originalMethod = class_getInstanceMethod(class, originalSelector);
Method replacementMethod = class_getInstanceMethod(class, replacementSelector);
BOOL didAddMethod =
class_addMethod(class,
originalSelector,
method_getImplementation(replacementMethod),
method_getTypeEncoding(replacementMethod));
if (didAddMethod) {
class_replaceMethod(class,
replacementSelector,
method_getImplementation(originalMethod),
method_getTypeEncoding(originalMethod));
} else {
method_exchangeImplementations(originalMethod, replacementMethod);
}
}
#pragma mark - Private
@interface XCTestObservationCenter (Private)
- (void)_addLegacyTestObserver:(id)observer;
@end
@implementation XCTestObservationCenter (Register)
/// Uses objc method swizzling to register `CurrentTestCaseTracker` as a test observer. This is necessary
/// because Xcode 7.3 introduced timing issues where if a custom `XCTestObservation` is registered too early
/// it suppresses all console output (generated by `XCTestLog`), breaking any tools that depend on this output.
/// This approach waits to register our custom test observer until XCTest adds its first "legacy" observer,
/// falling back to registering after the first normal observer if this private method ever changes.
+ (void)load {
if (class_getInstanceMethod([self class], @selector(_addLegacyTestObserver:))) {
// Swizzle -_addLegacyTestObserver:
swizzleSelectors([self class], @selector(_addLegacyTestObserver:), @selector(NMB_original__addLegacyTestObserver:));
} else {
// Swizzle -addTestObserver:, only if -_addLegacyTestObserver: is not implemented
swizzleSelectors([self class], @selector(addTestObserver:), @selector(NMB_original_addTestObserver:));
}
}
#pragma mark - Replacement Methods
/// Registers `CurrentTestCaseTracker` as a test observer after `XCTestLog` has been added.
- (void)NMB_original__addLegacyTestObserver:(id)observer {
[self NMB_original__addLegacyTestObserver:observer];
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
[self addTestObserver:[CurrentTestCaseTracker sharedInstance]];
});
}
/// Registers `CurrentTestCaseTracker` as a test observer after `XCTestLog` has been added.
/// This method is only used if `-_addLegacyTestObserver:` is not impelemented. (added in Xcode 7.3)
- (void)NMB_original_addTestObserver:(id<XCTestObservation>)observer {
[self NMB_original_addTestObserver:observer];
static dispatch_once_t onceToken;
dispatch_once(&onceToken, ^{
[self NMB_original_addTestObserver:[CurrentTestCaseTracker sharedInstance]];
});
}
@end