iOSプロジェクトのテストバンドルに存在するファイルを取得する ref: https://qiita.com/enomotok_/items/27d132969b41bcd26187

file0.txt

let path = Bundle.main.path(forResource: "foo", ofType: "json")
let data: NSData? = try? NSData(contentsOfFile: path!, options: .uncached)

file1.txt

let testBundle = Bundle(for: type(of: self))
let path = testBundle.url(forResource: "bar", withExtension: "json")
let data: NSData? = try? NSData(contentsOf: path!, options: .uncached)