pod install fails after adding UITesting target to project

I added a new UI testing bundle to my project, and now when I run pod install. I did not modify the Podfile, I just created the targets and made a few tests. My test target and the tests worked, I did not notice I had broken Cocoapods until later when branch switches necessitated a new pod install.

The error output instructed me to file and issue so here I am. I have redacted the name of my UI test target, it is not really ****UITests.

I rand gem install cocoapods to make sure I had the latest version.

### Error

```
RuntimeError - `PBXGroup` attempted to initialize an object with unknown ISA `PBXFileSystemSynchronizedRootGroup` from attributes: `{"isa"=>"PBXFileSystemSynchronizedRootGroup", "explicitFileTypes"=>{}, "explicitFolders"=>[], "path"=>"****UITests", "sourceTree"=>""}`
If this ISA was generated by Xcode please file an issue: https://github.com/CocoaPods/Xcodeproj/issues/new
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project/object.rb:359:in `rescue in object_with_uuid'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project/object.rb:349:in `object_with_uuid'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project/object.rb:300:in `block (2 levels) in configure_with_plist'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project/object.rb:299:in `each'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project/object.rb:299:in `block in configure_with_plist'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project/object.rb:296:in `each'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project/object.rb:296:in `configure_with_plist'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project.rb:272:in `new_from_plist'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project/object.rb:350:in `object_with_uuid'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project/object.rb:290:in `block in configure_with_plist'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project/object.rb:287:in `each'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project/object.rb:287:in `configure_with_plist'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project.rb:272:in `new_from_plist'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project.rb:213:in `initialize_from_file'
/Library/Ruby/Gems/2.6.0/gems/xcodeproj-1.24.0/lib/xcodeproj/project.rb:113:in `open'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/installer/analyzer.rb:1194:in `block (2 levels) in inspect_targets_to_integrate'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/installer/analyzer.rb:1193:in `each'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/installer/analyzer.rb:1193:in `block in inspect_targets_to_integrate'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/user_interface.rb:64:in `section'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/installer/analyzer.rb:1188:in `inspect_targets_to_integrate'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/installer/analyzer.rb:107:in `analyze'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/installer.rb:422:in `analyze'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/installer.rb:244:in `block in resolve_dependencies'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/user_interface.rb:64:in `section'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/installer.rb:243:in `resolve_dependencies'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/installer.rb:162:in `install!'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/command/install.rb:52:in `run'
/Library/Ruby/Gems/2.6.0/gems/claide-1.1.0/lib/claide/command.rb:334:in `run'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/lib/cocoapods/command.rb:52:in `run'
/Library/Ruby/Gems/2.6.0/gems/cocoapods-1.15.2/bin/pod:55:in `'
/usr/local/bin/pod:23:in `load'
/usr/local/bin/pod:23:in `'
```

――― TEMPLATE END ――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――――

[!] Oh no, an error occurred.

Search for existing GitHub issues similar to yours:
https://github.com/CocoaPods/CocoaPods/search?q=%60PBXGroup%60+attempted+to+initialize+an+object+with+unknown+ISA+%60PBXFileSystemSynchronizedRootGroup%60+from+attributes%3A+%60%7B%22isa%22%3D%3E%22PBXFileSystemSynchronizedRootGroup%22%2C+%22explicitFileTypes%22%3D%3E%7B%7D%2C+%22explicitFolders%22%3D%3E%5B%5D%2C+%22path%22%3D%3E%22****UITests%22%2C+%22sourceTree%22%3D%3E%22%3Cgroup%3E%22%7D%60%0AIf+this+ISA+was+generated+by+Xcode+please+file+an+issue%3A+https%3A%2F%2Fgithub.com%2FCocoaPods%2FXcodeproj%2Fissues%2Fnew&type=Issues

If none exists, create a ticket, with the template displayed above, on:
https://github.com/CocoaPods/CocoaPods/issues/new

Be sure to first read the contributing guide for details on how to properly submit a ticket:
https://github.com/CocoaPods/CocoaPods/blob/master/CONTRIBUTING.md

Don't forget to anonymize any private data!

Looking for related issues on cocoapods/cocoapods...
Searching for inspections failed: undefined method `map' for nil:NilClass