I am trying to mock the ```any<File>().outpu...

# mockk

[Ravin Jain]

I am trying to mock the

any<File>().outputStream()

I am trying this

val mockOs = mockk<FileOutputStream>()
mockkStatic("kotlin.io.FilesKt__FileReadWriteKt")
mockkStatic(Files::class)
val resultFile = mockk<File>()
every { resultFile.path } answers {"somepath"}
every { any<File>().outputStream() } returns mockOs

But always gets this error

(No such file or directory)
java.io.FileNotFoundException:  (No such file or directory)
	at java.base/java.io.FileOutputStream.open0(Native Method)
	at java.base/java.io.FileOutputStream.open(FileOutputStream.java:298)
	at java.base/java.io.FileOutputStream.<init>(FileOutputStream.java:237)
	at java.base/java.io.FileOutputStream.<init>(FileOutputStream.java:187)

Any idea ?

[Mattia Tommasone]

yes 🙂
i think what you should be doing is

every { resultFile.outputStream() } returns mockOs

You cannot use any<File>() that way: any() is to match arguments, not to describe mocks

[Ravin Jain]

Tried that getting the same error

[ephemient]

1. you can avoid the string reference to the file facade class with mockkStatic(File::outputStream)
2. in this case, any<File>().outputStream() is correct because the File is the receiver of an extension function, which makes it just like a normal argument in every way except syntax
3. I'm pretty sure the problem here is that FileOutputStream is from the system classloader and cannot be mocked

[ephemient]

if at all possible, you'd be better off switching to java.nio.file and using a virtual filesystem - then you don't even have to worry about mocking

[Matteo Mirk]

or you can use this https://github.com/google/jimfs or similar libraries for testing purposes

[ephemient]

yes, that's basically my suggestion: jimfs is a virtual java.nio.file filesystem

[ephemient]

it's not the only one, there's also http://commons.apache.org/proper/commons-vfs/ but I've never used it

[Matteo Mirk]

Oh ok thanks for clarifying. Wasn’t aware of this detail, I just suggested the lib because I used it once in a project and was very useful

[Ravin Jain]

I was able to resolve this by using TemporaryFolder from junit

[Matteo Mirk]

nice, TemporaryFolder is good, but consider that it interacts with your filesystem. If you use one of the libs cited above, you’ll get the same result but all in-memory

[ephemient]

I wouldn't consider TemporaryFolder for a unit test due to its interaction with the real filesystem, but it can be useful