Added array extensions test

src/test/kotlin/app/extensions/ArrayExtensionsKtTest.kt

@@ -0,0 +1,23 @@
+package app.extensions
+
+import org.junit.jupiter.api.Test
+
+import org.junit.jupiter.api.Assertions.*
+
+internal class ArrayExtensionsTest {
+    @Test
+    fun matchingIndexes() {
+        val array = arrayOf<Int?>(0, 1, 2, 3, null, 5, 6, null)
+        val result = array.matchingIndexes { it == null }
+        assertEquals(result.count(), 2)
+        assertEquals(result[0], 4)
+        assertEquals(result[1], 7)
+    }
+
+    @Test
+    fun matchingIndexes_empty_array() {
+        val array = arrayOf<Int>()
+        val result = array.matchingIndexes { it > 0 }
+        assertEquals(result.count(), 0)
+    }
+}