Extract swizzleSelectors function

Author: phatblat

Sources/Nimble/Adapters/ObjectiveC/XCTestObservationCenter+Register.m

@@ -2,38 +2,14 @@
 #import <XCTest/XCTest.h>
 #import <objc/runtime.h>
 
-#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:
-        [self swizzleSelector:@selector(_addLegacyTestObserver:) withSelector:@selector(NMB_original__addLegacyTestObserver:)];
-    } else {
-        // Swizzle -addTestObserver:, only if -_addLegacyTestObserver: is not implemented
-        [self swizzleSelector:@selector(addTestObserver:) withSelector:@selector(NMB_original_addTestObserver:)];
-    }
-}
-
 #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)swizzleSelector:(SEL)originalSelector withSelector:(SEL)replacementSelector {
-    Class class = [self class];
-
+void swizzleSelectors(Class class, SEL originalSelector, SEL replacementSelector) {
     Method originalMethod = class_getInstanceMethod(class, originalSelector);
     Method replacementMethod = class_getInstanceMethod(class, replacementSelector);
 
@@ -53,6 +29,29 @@ + (void)swizzleSelector:(SEL)originalSelector withSelector:(SEL)replacementSelec
     }
 }
 
+#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.