add test for #3946

tests/unit/src/unit/issues/Issue3946.hx

@@ -0,0 +1,10 @@
+package unit.issues;
+
+class Issue3946 extends Test {
+    #if cs
+    function test() {
+        var arr = cs.Lib.arrayAlloc(10);
+        eq(arr.length, 10);
+    }
+    #end
+}