Mock top-level and extension functions #

Top-level functions #

Kotlin lets you write functions that don’t belong to any class or object, called top-level functions. These calls are translated to static methods in Java, and a special Java class is generated to hold the functions. These top-level functions can be mocked using mockkStatic. You just need to import the function and pass a reference as the argument.

import pkg.toplevelFunction

mockkStatic(::toplevelFunction)
every { toplevelFunction() } returns "top"

Extension functions #

Depending on where an extension function is located, it may correspond to a top-level function or a class member. If placed inside a class, the extension function is attached to that class and can be mocked using the with method.

// TODO val mock = ...

with (mock) {
  every { any<Type>().extensionFunction() } returns "result"
}

If the extension function is inside an object, the code is similar but the object needs to be mocked first.

When the extension function is in the top-level of a file, it can be mocked like other top-level functions using mockkStatic.