How to stub varargs in Mockito to match only one argument

Hugh :

I'd like to stub some code so that a vararg method returns true when one of the arguments matches a specific value. For example, given the existing code that I can't change:

(Using Kotlin here, but I figure this applies to any Java situation.)

class Foo {
    fun bar(vararg strings : String) : Boolean {
        // Iterates `strings` and returns true when one satisfies some criteria
    }
}

... I want to write stub code similar to this:

val foo = Foo()
whenever(foo.bar(eq("AAA"))).thenReturn(true)

This works fine when the call is exactly foo.bar("AAA").

However, there are times when the code under test makes the call foo.bar("AAA", "BBB"), and in those cases, it fails.

How can I revise my stub code so it works when any number of varargs are passed in the call?

Edit Flagged as a possible duplicate; in that case, the scenario contemplates the complete omission of the varargs in the call. Here, I'm trying to match one specific element of the varargs array.

Lino :

You have to stub your method 2 times. First the least specific stub:

val foo = Foo()
whenever(foo.bar(any())).thenReturn(false) // or whatever you want to return/throw here

And then the more specific single argument method:

whenever(foo.bar(eq("AAA"))).thenReturn(true)

---

After your comment you may aswell use something like this (using Java this time):

when(foo.bar(any())).thenAnswer(invocation -> {
    for (Object argument : invocation.getArguments()) {
        if ("AAA".equals(argument)) return true;
    }
    return false;
});

---

And the same in Kotlin

whenever(foo.bar(any()).thenAnswer {
    it.arguments.contains("AAA")
}