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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Default value (object of type Proxy) can give false positives when testing validations","articleBody":"Hi,\r\nThanks for an amazing lib! It definitely makes work with JavaScript more human-friendly! :)\r\nI've bumped into a small difference with NSubstitute behaviour and wondering if maybe I just can't find a proper syntax to turn on or off a setting to make things work similarly to what I used to in C#:)\r\n\r\nSo what I'm trying to achieve.\r\nI have an interface\r\n```\r\ninterface Worker {\r\n   SUPPORTED_WORK: number[];\r\n   doSomething();\r\n}\r\n```\r\n\r\nAnd this kind of usage of the interface in some service:\r\n```\r\nconstructor (private worker: Worker) {}\r\n....\r\n\r\npublic someServiceMethod(workId) {\r\n   if (!this.worker.SUPPORTED_WORK.includes(workId)) {\r\n      throw Error(\"Invalid work\");\r\n   }\r\n...\r\n```\r\n\r\nCurrently, when I setup a test to cover this validation, if I don't specifying any behaviour for `SUPPORTED_WORK` property, the test automatically passes.\r\n```\r\nconst worker = Substitute.for\u003cWorker\u003e();\r\nconst service = new MyService(worker);\r\n\r\nservice.someServiceMethod(42);\r\n...//some test logic\r\n```\r\n\r\nBasing on the NSubstitute behaviour, I would expect this usage to throw an error, since the `SUPPORTED_WORK` property is missing or `.include` behaviour returns null or something like that by default.\r\n\r\nAt the moment, if the mock is unset `.include(workId)` returns a Proxy object, which is truthy. It makes the if-statement pass and giving a false positive in my test.\r\nEven if I wrap this check into some method like:\r\n```\r\n   if (!this.worker.isWorkSupported(workId)) {\r\n      throw Error(\"Invalid work\");\r\n   }\r\n```\r\nThe issue remains.\r\n\r\nWondering, if I can just tweak some setting to prevent false positives in that kind of checks when I miss to setup returns of my mock?","author":{"url":"https://github.com/SergiiVolodkoWorking","@type":"Person","name":"SergiiVolodkoWorking"},"datePublished":"2021-01-13T20:54:42.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":4},"url":"https://github.com/165/FluffySpoon.JavaScript.Testing.Faking/issues/165"}