Test just the assignement operator as suggested

test/hotspot/gtest/nmt/test_nmt_reserved_region.cpp

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+/*
+ * Copyright (c) 2023 SAP SE. All rights reserved.
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+#include "precompiled.hpp"
+#include "runtime/os.hpp"
+#include "services/memTracker.hpp"
+#include "services/virtualMemoryTracker.hpp"
+#include "unittest.hpp"
+
+// Tests the assignment operator of ReservedMemoryRegion
+TEST_VM(NMT, ReservedRegionCopy) {
+  address dummy1 = (address)0x10000000;
+  ReservedMemoryRegion region1(dummy1, os::vm_page_size(), CALLER_PC);
+  region1.add_committed_region(dummy1, os::vm_page_size(), CALLER_PC);
+  region1.set_flag(mtThreadStack);
+  region1.set_call_stack(NativeCallStack(&dummy1, 1));
+  address dummy2 = (address)0x20000000;
+  ReservedMemoryRegion region2(dummy2, os::vm_page_size(), CALLER_PC);
+  region2.add_committed_region(dummy2, os::vm_page_size(), CALLER_PC);
+  region2.set_flag(mtCode);
+  region2.set_call_stack(NativeCallStack(&dummy2, 1));
+
+  region2 = region1;
+
+  CommittedRegionIterator itr = region2.iterate_committed_regions();
+  const CommittedMemoryRegion* rgn = itr.next();
+  ASSERT_EQ(rgn->base(), dummy1); // Now we should see dummy1
+  ASSERT_EQ(region2.flag(), mtThreadStack); // Should be correct flag
+  ASSERT_EQ(region2.call_stack()->get_frame(0), dummy1); // Check the stack
+  rgn = itr.next();
+  ASSERT_EQ(rgn, (const CommittedMemoryRegion*)nullptr); // and nothing else
+}
+