How to mock local variables using MockK

Question

I have the following simplified code

class Foo() {
    suspend fun bar() {
        val headers = AtomicReference(Metadata())
        val metadata = headers.get()
        if (metadata.keys().size > 0) { // I want it to return a value specified in the test file
            // ...
    }
}

How can I mock AtomicReference or Metadata so that for example headers.get().keys().size returns a specified value and not the real one?

score 3 · Accepted Answer · answered Dec 06 '21 at 19:10

You can mock the constructor of Metadata using Constructor Mocks:

mockkConstructor(Metadata::class)

every { anyConstructed<Metadata>().keys() } returns mockedKeys

Note that mockedKeys of keys is your test data.

See https://mockk.io/#constructor-mocks

Additionally, try to architect your code in a fashion that you don't need to mock any constructor (like for example using inversion of control), you will see that it pays dividends when testing.

How to mock local variables using MockK

1 Answers1