test: Data race in testReportFullyDisplayed (#5499)

Setting a new TestTimeToDisplayTracker to the SentryDependencyContainer
directly after starting the SDK led to a data race in
sentry_sdkInitProfilerTasks, because sentry_sdkInitProfilerTasks
accesses the TimeToDisplayTracker on a BG thread. This is fixed now by
setting the TestTimeToDisplayTracker to the SentryDependencyContainer
before starting the SDK.

Author: philipphofmann

Tests/SentryTests/SentrySDKTests.swift

@@ -728,13 +728,14 @@ class SentrySDKTests: XCTestCase {
     func testReportFullyDisplayed() {
         fixture.options.enableTimeToFullDisplayTracing = true
 
-        SentrySDK.start(options: fixture.options)
-
         let testTTDTracker = TestTimeToDisplayTracker(waitForFullDisplay: true)
-
         let performanceTracker = Dynamic(SentryDependencyContainer.sharedInstance().uiViewControllerPerformanceTracker)
         performanceTracker.currentTTDTracker = testTTDTracker
 
+        // Start SDK after setting up the tracker to ensure we're changing the tracker during it's initialization,
+        // because some initialization logic happens on a BG thread and we would end up in a race condition.
+        SentrySDK.start(options: fixture.options)
+
         SentrySDK.reportFullyDisplayed()
 
         XCTAssertTrue(testTTDTracker.registerFullDisplayCalled)