From c81750d433ebcb4830af87924220d1276eeeb979 Mon Sep 17 00:00:00 2001
From: Mark Villacampa <MarkVillacampa@users.noreply.github.com>
Date: Fri, 5 Apr 2024 22:40:22 +0200
Subject: [PATCH] Register test observer in main queue (#834)

---
 Sources/SnapshotTesting/AssertSnapshot.swift | 18 ++++++++++++------
 1 file changed, 12 insertions(+), 6 deletions(-)

diff --git a/Sources/SnapshotTesting/AssertSnapshot.swift b/Sources/SnapshotTesting/AssertSnapshot.swift
index 552077e49..cd25d88f3 100644
--- a/Sources/SnapshotTesting/AssertSnapshot.swift
+++ b/Sources/SnapshotTesting/AssertSnapshot.swift
@@ -371,18 +371,24 @@ func sanitizePathComponent(_ string: String) -> String {
 // We need to clean counter between tests executions in order to support test-iterations.
 private class CleanCounterBetweenTestCases: NSObject, XCTestObservation {
   private static var registered = false
-  private static var registerQueue = DispatchQueue(
-    label: "co.pointfree.SnapshotTesting.testObserver")
 
   static func registerIfNeeded() {
-    registerQueue.sync {
-      if !registered {
-        registered = true
-        XCTestObservationCenter.shared.addTestObserver(CleanCounterBetweenTestCases())
+    if Thread.isMainThread {
+      doRegisterIfNeeded()
+    } else {
+      DispatchQueue.main.sync { 
+        doRegisterIfNeeded()
       }
     }
   }
 
+  private static func doRegisterIfNeeded() {
+    if !registered {
+      registered = true
+      XCTestObservationCenter.shared.addTestObserver(CleanCounterBetweenTestCases())
+    }
+  }
+
   func testCaseDidFinish(_ testCase: XCTestCase) {
     counterQueue.sync {
       counterMap = [:]