# iOS 9 upgrade: Why did my unit tests grind to a halt?

DevFeed: [iOS 9 upgrade: Why did my unit tests grind to a halt?](<https://devfeed.tech/articles/ios-9-upgrade-why-did-my-unit-tests-grind-to-a-halt-15723.md>)

Original publisher: [Read original article](<https://developer.squareup.com/blog/ios-9-upgrade-why-did-my-unit-tests-grind-to-a-halt>)

Author: Square Engineering

Published: 2016-04-27T16:11:00Z

Content type: article

Language: en

Sources: [Square Corner Blog RSS Feed](<https://devfeed.tech/sources/square-corner-blog-rss-feed.md>)

Topics: [iOS](<https://devfeed.tech/topics/ios.md>), [SDK](<https://devfeed.tech/topics/sdk.md>)

Tags: [developer](<https://devfeed.tech/tags/developer.md>), [engineering](<https://devfeed.tech/tags/engineering.md>), [ios](<https://devfeed.tech/tags/ios.md>), [issue](<https://devfeed.tech/tags/issue.md>), [locking](<https://devfeed.tech/tags/locking.md>), [queue](<https://devfeed.tech/tags/queue.md>), [tests](<https://devfeed.tech/tags/tests.md>), [unit-tests](<https://devfeed.tech/tags/unit-tests.md>), [upgrade](<https://devfeed.tech/tags/upgrade.md>)

## AI overview

An investigation into unit-test slowdowns and intermittent failures after Square Register moved from the iOS 8 to iOS 9 SDK. The article describes narrowing the problem to test-suite scale, queues, and a timing-sensitive test failure.

## Source excerpt

An investigation into why upgrading from iOS 8 to 9 SDK led to slow tests.