Mockk Missing calls inside every { ... } block

It seems to be a Mockk opened issue: https://github.com/mockk/mockk/issues/182

2 possible quick fixes (pick one):

1. Run the Instrumented Tests in an emulator >= Android-P
2. Set Foo class as open (and the method(s) you want to mock too)

Try to check the official guide and see what is missing.

In my case, I tried to mock an extension in Kotlin but missed the mockkStatic

fun Date.asMyTime() : DateTime = DateTime(this, DateTimeZone.getDefault())

mockkStatic("packageName.FileNameKt") // This is what I was missing
every {
    DateTime().asMyTime()
} returns mock(DateTime::class.java)