Add some simple tests on HashPMap

compiler/testData/codegen/boxWithStdlib/hashPMap/manyNumbers.kt

@@ -0,0 +1,47 @@
+import java.util.*
+import kotlin.reflect.jvm.internal.pcollections.HashPMap
+import kotlin.test.*
+
+fun digitSum(number: Int): Int {
+    var x = number
+    var ans = 0
+    while (x != 0) {
+        ans += x % 10
+        x /= 10
+    }
+    return ans
+}
+
+val N = 1000000
+
+fun box(): String {
+    var map = HashPMap.empty<Int, Any>()!!
+
+    for (x in 1..N) {
+        map = map.plus(x, digitSum(x))!!
+    }
+
+    assertEquals(N, map.size())
+    
+    // Check in reverse order just in case
+    for (x in N downTo 1) {
+        assertTrue(map.containsKey(x), "Not found: $x")
+        assertEquals(digitSum(x), map[x], "Incorrect value for $x")
+    }
+
+    // Delete in random order
+    val list = (1..N).toCollection(ArrayList<Int>())
+    Collections.shuffle(list, Random(42))
+    for (x in list) {
+        map = map.minus(x)!!
+    }
+
+    assertEquals(0, map.size())
+
+    for (x in 1..N) {
+        assertFalse(map.containsKey(x), "Incorrectly found: $x")
+        assertEquals(null, map[x], "Incorrectly found value for $x")
+    }
+
+    return "OK"
+}