Fix the broken tests for SKAN v2

Summary:
- Fix the broken tests on master.
- The DateComponents takes daylight saving time into account, so when you ask to subtract 35 days, it doesn't subtract exactly 35×24×60×60 seconds. Instead, it goes back 35 calendar days, which due to daylight saving time changes, can result in a slightly different number of total seconds.

Differential Revision: D51377252

fbshipit-source-id: ec579ee3890988ac3dc564c095f5ae4f71134519

FBSDKCoreKit/FBSDKCoreKitTests/Internal/AppEvents/SKAdNetwork/SKAdNetworkReporterTestsV2.swift

@@ -452,15 +452,11 @@ final class SKAdNetworkReporterTestsV2: XCTestCase {
   }
 
   func testGetCurrentPostbackWindow() {
-    // 1st postback window, 0-2 days
-    var addComponents = DateComponents()
-    addComponents.day = -1
-    addComponents.hour = -23
-    addComponents.minute = -59
-    addComponents.second = -59
+    let currentDate = Date()
 
-    let calendar = Calendar(identifier: .gregorian)
-    var expiredDate = calendar.date(byAdding: addComponents, to: Date())
+    // 1st postback window, 0-2 days
+    var secondsInPast = 2 * 24 * 60 * 60 - 1
+    var expiredDate = currentDate.addingTimeInterval(-TimeInterval(secondsInPast))
     userDefaultsSpy.set(
       expiredDate,
       forKey: "com.facebook.sdk:FBSDKSettingsInstallTimestamp"
@@ -471,11 +467,8 @@ final class SKAdNetworkReporterTestsV2: XCTestCase {
     )
 
     // 2nd postback window, 3-7 days
-    addComponents.day = -6
-    addComponents.hour = -23
-    addComponents.minute = -59
-    addComponents.second = -59
-    expiredDate = calendar.date(byAdding: addComponents, to: Date())
+    secondsInPast = 7 * 24 * 60 * 60 - 1
+    expiredDate = currentDate.addingTimeInterval(-TimeInterval(secondsInPast))
     userDefaultsSpy.set(
       expiredDate,
       forKey: "com.facebook.sdk:FBSDKSettingsInstallTimestamp"
@@ -486,11 +479,8 @@ final class SKAdNetworkReporterTestsV2: XCTestCase {
     )
 
     // 3rd postback window, 8-35 days
-    addComponents.day = -34
-    addComponents.hour = -23
-    addComponents.minute = -59
-    addComponents.second = -59
-    expiredDate = calendar.date(byAdding: addComponents, to: Date())
+    secondsInPast = 35 * 24 * 60 * 60 - 1
+    expiredDate = currentDate.addingTimeInterval(-TimeInterval(secondsInPast))
     userDefaultsSpy.set(
       expiredDate,
       forKey: "com.facebook.sdk:FBSDKSettingsInstallTimestamp"