Fix capturing varargs with Mockito 5 (#490)

Fixes #474

Author: lukas-krecan

mockito-kotlin/src/main/kotlin/org/mockito/kotlin/ArgumentCaptor.kt

@@ -27,6 +27,7 @@ package org.mockito.kotlin
 
 import org.mockito.kotlin.internal.createInstance
 import org.mockito.ArgumentCaptor
+import java.lang.reflect.Array
 import kotlin.reflect.KClass
 
 /**
@@ -195,8 +196,21 @@ class KArgumentCaptor<out T : Any?>(
 
     @Suppress("UNCHECKED_CAST")
     fun capture(): T {
-        return captor.capture() ?: createInstance(tClass) as T
+        // Special handling for arrays to make it work for varargs
+        // In Kotlin we want have to capture vararg like this `verify(m).methodName(*captor.capture())` to make the types work
+        // If we return null for array types, the spread `*` operator will fail with NPE
+        // If we return empty array, it will fail in MatchersBinder.validateMatchers
+        // In Java, `captor.capture` returns null and so the method is called with `[null]`
+        // In Kotlin, we have to create `[null]` explicitly.
+        // This code-path is applied for non-vararg array arguments as well, but it seems to work fine.
+        return captor.capture() ?: if (tClass.java.isArray) {
+            singleElementArray()
+        } else {
+            createInstance(tClass)
+        } as T
     }
+
+    private fun singleElementArray(): Any? = Array.newInstance(tClass.java.componentType, 1)
 }
 
 val <T> ArgumentCaptor<T>.firstValue: T

tests/src/test/kotlin/test/ArgumentCaptorTest.kt

@@ -226,4 +226,88 @@ class ArgumentCaptorTest : TestBase() {
             }
         }
     }
+
+    @Test
+    fun argumentCaptor_vararg() {
+        /* Given */
+        val m: Methods = mock()
+
+        /* When */
+        m.varargBooleanResult("a", "b", "c")
+
+        /* Then */
+        val captor = argumentCaptor<Array<String>>()
+        verify(m).varargBooleanResult(*captor.capture())
+        expect(captor.firstValue.toList()).toBe(listOf("a", "b", "c"))
+    }
+
+    @Test
+    fun argumentCaptor_empty_vararg() {
+        /* Given */
+        val m: Methods = mock()
+
+        /* When */
+        m.varargBooleanResult()
+
+        /* Then */
+        val captor = argumentCaptor<Array<String>>()
+        verify(m).varargBooleanResult(*captor.capture())
+        expect(captor.firstValue.toList()).toBe(listOf())
+    }
+
+    @Test
+    fun argumentCaptor_arg_vararg() {
+        /* Given */
+        val m: Methods = mock()
+
+        /* When */
+        m.argAndVararg("first", "a", "b", "c")
+
+        /* Then */
+        val captor = argumentCaptor<Array<String>>()
+        verify(m).argAndVararg(any(), *captor.capture())
+        expect(captor.firstValue.toList()).toBe(listOf("a", "b", "c"))
+    }
+
+    @Test
+    fun argumentCaptor_intarray() {
+        /* Given */
+        val m: Methods = mock()
+
+        /* When */
+        m.intArray(intArrayOf(1, 2, 3))
+
+        /* Then */
+        val captor = argumentCaptor<IntArray>()
+        verify(m).intArray(captor.capture())
+        expect(captor.firstValue.toList()).toBe(listOf(1, 2, 3))
+    }
+
+    @Test
+    fun argumentCaptor_array() {
+        /* Given */
+        val m: Methods = mock()
+
+        /* When */
+        m.stringArray(arrayOf("a", "b", "c"))
+
+        /* Then */
+        val captor = argumentCaptor<Array<String>>()
+        verify(m).stringArray(captor.capture())
+        expect(captor.firstValue.toList()).toBe(listOf("a", "b", "c"))
+    }
+
+    @Test
+    fun argumentCaptor_empty_array() {
+        /* Given */
+        val m: Methods = mock()
+
+        /* When */
+        m.stringArray(arrayOf())
+
+        /* Then */
+        val captor = argumentCaptor<Array<String>>()
+        verify(m).stringArray(captor.capture())
+        expect(captor.firstValue.toList()).toBe(listOf())
+    }
 }

tests/src/test/kotlin/test/Classes.kt

@@ -70,6 +70,8 @@ interface Methods {
     fun nullableStringResult(): String?
     fun builderMethod(): Methods
     fun varargBooleanResult(vararg values: String): Boolean
+    fun stringArray(a: Array<String>)
+    fun argAndVararg(s: String, vararg a: String)
 
     fun nonDefaultReturnType(): ExtraInterface
 }